?,^'/-2X. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  122. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


THE  ARGENTINE  ANT 


WILMON  NEWELL,  M.  S., 


T.  C.  BARBER,  B.  S.  A. 


Issued  June  26,  1913. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1913. 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  I. 


U.  S.  DEPARTMENT  OF   AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  122. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


THE  ARGENTINE  ANT 


BY 

WILMON  NEWELL,  M.S., 

AXD 

T.  C.  BARBER,  B.  S.  A. 


Issued  June  26,  1913. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1913. 


B  UREA  U  OF  ENTOMOLOGY. 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 
C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 
R.  S.  Clifton,  Executive  Assistant. 
W.  P.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 

A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
Rolla  P.  Currie,  in  charge  of  editorial  work. 
Mabel  Colcord,  in  charge  of  library. 

Southern  Field  Crop  Insect  Investigations. 

W.  D.  Hunter,  in  charge. 

W.  D.  Pierce,  J.  D.  Mitchell,  G.  D.  Smith,  E.  A.  McGregor,  Harry  Pinkus, 
B.  R.  Coad,  G.  N.  Wolcott,  W.  A.  Thomas,  R.  W.  Moreland,  C.  E.  Hester, 
engaged  in  cotton-boll  weevil  investigations. 

F.  C  Bishopp,  A.  H.  Jennings,  H.  P.  Wood,  W.  V.  King,  engaged  in  tick  investi- 
gations. 

A.  C  Morgan,  G.  A.  Runner,  S.  E.  Crumb,  D.  C.  Parman,  engaged  in  tobacco  insect 

investigations. 
T.  E.  Holloway,  E.  R.  Barber,  engaged  in  sugar  cane  insect  investigations. 
J.  L.  Webb,  engaged  in  rice  insect  investigations. 

R.  A.  Cooley,  D.  L.  Van  Dine,  A.  F.  Conradi,  C.  C.  Krumbhaar,  collaborators. 
2 


LETTER  OF  TRANSMITTAL 


U.  S.  Department  of  Agriculture, 

Bureau  of  Entomology, 
TVashingtorij  B.C.,  January  2,  1913. 
Sir:  I  have  the  honor  to  transmit  herewith  and  to  recommend 
for  publication  as  Bulletin  No.  122,  of  the  Bureau  of  Entomology, 
a  manuscript  entitled  "The  Argentine  Ant,"  by  Mr.  Wilmon  Newell, 
formerly  a  collaborator,  and  Mr.  T.  C.  Barber,  formerly  an  agent  of 
this  bureau. 

The  Argentine  ant  is  an  imported  pest  of  great  importance.  It 
is  unique  among  injurious  insects  of  this  country  in  the  diversity  of 
the  damage  that  it  causes.  It  is  not  only  a  household  pest  of  the 
first  rank,  but  it  affects  materially  the  interests  of  sugar  planters, 
orange  growers,  and  others.  The  territory  infested  by  this  ant  is 
being  rapidly  extended.  For  all  of  these  reasons  it  is  important  that 
there  be  placed  on  record  a  full  account  of  the  studies  that  have  been 
conducted  regarding  it. 

The  work  upon  which  this  manuscript  is  based  was  begun  by  Mr. 
Newell  as  secretary  of  the  Louisiana  State  Crop  Pest  Commission. 
Later  Mr.  Newell  continued  the  work  as  a  collaborator  in  this  bureau, 
and  Mr.  Barber,  an  agent  of  the  bureau,  but  working  under  Mr. 
Newell' s  direction,  added  to  the  results  obtained. 
Respectfully, 

L.  O.  Howard, 
Entomologist  and  Chief  of  Bureau. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 


CONTENTS 


Page. 

Introduction 9 

General  considerations 10 

History  and  distribution 11 

Introduction  into  Louisiana 12 

Present  distribution  in  the  Southern  States 14 

Occurrence  and  distribution  in  California 15 

Area  of  ultimate  infestation 16 

Common  name 18 

Means  of  dispersion 19 

Natural  spread 19 

Flight 19 

Dispersion  by  streams 20 

Artificial  dissemination 20 

Economic  importance 22 

Systematic  position 26 

Description  of  the  species. 27 

Resemblance  to  other  ants 30 

Methods  of  study 32 

Establishing  colonies  for  study 36 

Life  history 38 

The  egg 38 

Period  of  incubation 39 

The  larva 40 

Duration  of  the  larval  stage 41 

The  pupa 42 

The  worker  pupa 42 

The  male  pupa 43 

The  queen  pupa 44 

The  callow  or  teneral  stage 45 

Time  required  for  complete  development 45 

The  adults 46 

The  worker 46 

Length  of  life 47 

The  male 47 

The  queen 48 

The  virgin  queen 48 

The  dealated,  or  fertile,  queen 49 

The  colony  as  a  whole : 51 

Seasonal  history 51 

Winter  colonies 51 

Summer  colonies 52 

Compound  colonies  or  communities 54 

5 


b  CONTEXTS. 

The  colony  as  a  whole — Continued.  Page 

Migrations 54 

General  migration  or  dispersion 54 

Migration  to  food  supply 54 

Concentrating  migration 5 4 

Divisional  migration ;,:, 

Nests  or  natural  formicaries ,",;, 

Underground  nests 56 

Wet-weather  nests  or  sheds 56 

General  observations 57 

Aversion  to  light 57 

Sense  of  smell 57 

Sight 57 

Hearing 58 

Cannibalism 58 

Sanitation 59 

Rate  of  travel •. 59 

Storage  of  food GO 

Relations  with  other  Arthropoda 61 

Formicidse <;  ] 

Coccidae  and  Aphididse 62 

List  of  Coccidae  and  ApMdid;e  attended  by  the  Argentine  ant 66 

Antagonism  toward  other  insects 66 

The  Argentine  ant  and  the  boll  weevil 68 

Beneficial  aspects  of  the  ant's  activities 69 

Symbiotic  relations 71 

Inquilines 72 

Natural  control 72 

Natural  enemies 72 

Insects  and  spiders 72 

Birds 73 

Experiments  with  Pediculoides 73 

Experiments  with  fungous  diseases 75 

Low  temperatures 76 

Floods 76 

Methods  of  repression 7ii 

Experiments  with  repellents 78 

Corrosive  sublimate  and  ' '  ant  tapes  " 80 

Experiments  with  fumigants  and  contact  insecticides 81 

Experiments  with  poisons 84 

Control  of  the  ant  in  residences 87 

Control  of  the  ant  in  apiaries 88 

Control  of  the  ant  in  orange  groves 91 

Method  of  dissemination  in  the  orange  section 93 

Experiments  in  the  orange  groves 94 

Experiments  with  winter  trap  boxes 95 

Bibliography 97 


ILLUSTRATIONS. 


PLATES. 

Page. 

Plate  I.  Argentine  ants  upon  a  tea  table Frontispiece. 

II.  A  small  colony  of  Argentine  ants  as  seen  in  one  of  the  artificial  for- 
micaries    32 

III.  "Formicarium,"  or  special  insectary,  constructed  and  equipped  for 

the  study  of  the  Argentine  ant 36 

IV.  Immature  stages  of  the  Argentine  ant 40 

V.  Wet- weather  nest  or  shed,  erected  by  Argentine  ants  during  rainy 

weather 56 

VI.  Orange  tree  after  exposure  to  Argentine  ants  for  three  seasons 64 

VII.  Beehive  on  ant-proof  hive  stand,  the  latter  resting  upon  a  concrete 

block 88 

VIII.  Orange  orchard  dying  as  a  result  of  infestation  by  the  Argentine  ant.  92 
IX.  Batture  of  the  Mississippi  River  50  miles  below  New  Orleans,  over- 
grown with  willows  and  heavily  infested  by  the  Argentine  ant 92 

X.  Siphon,  pumping  plant,  and  barrier  ditch  used  in  limiting  the  spread 

of  the  Argentine  ant 92 

XI.  Bridges  which  the  Argentine  ant  can  not  cross 92 

XII.  Trap  box  and  fumigating   cover  for  destruction   of  Argentine  ant 

while  in  winter  quarters 96 

XIII.  Orange  grove  in  which  campaign  was  waged  against  the  Argentine 

ant — appearance  of  the  grove  after  recovery 96 

TEXT   FIGURES. 

Fig.  1.  Map  of  Alabama,  Mississippi,  and  Louisiana,  showing  counties  in  the 

Southern  States  which  are  infested  by  the  Argentine  ant 14 

2.  Distribution  of  the  Argentine  ant  in  California 16 

3.  Injury  to   the  stand   of    sugar  cane    by  the   sugar-cane   mealy-bug 

(Pseudococcus  calceolarise) ,  which  is  attended  by  the  Argentine  ant..  24 

4.  Sugar-cane  mealy-bugs  on  sugar  cane 25 

5.  Covering  constructed  by  the  Argentine  ant  to  protect  the  mealy-bugs. .  26 

6.  The  Argentine  ant,  adult  forms 28 

7.  Artificial  formicary  or  cage  used  in  studying  the  Argentine  ant 33 

8.  Artificial  formicary  with  parts  assembled  ready  for  use 34 

9.  Entrance  of  artificial  formicary  shown  in  figures  7  and  8 35 

10.  Argentine  ant  removing  pupa  of  sorghum  midge  from  a  head  of  sorghum .  70 

11.  Ant-proof  hive  stand,  upturned,  showing  method  of  construction 90 

12.  Ant-proof  hive  stand,  sectional  view 91 

13.  Ant-proof  hive  stand,  from  above,  showing  construction 92 

7 


THE  ARGENTINE  ANT. 


INTRODUCTION. 

The  Argentine  ant  {Iridomyrmex  Jiumilis  Mayr),  which  is  made  the 
subject  of  the  present  paper,  is  the  first  among  the  Formicidae  to  attain 
the  front  rank  among  injurious  insects  in  the  United  States.  In  its 
field  the  Argentine  ant  is  not  excelled  in  destructiveness  by  even  the 
gipsy  moth,  the  boll  weevil,  or  the  San  Jose  scale.  Though  this  ant 
is  limited  as  yet  to  comparatively  small  areas,  the  observations  and 
experience  of  the  authors  fully  convince  them  that  future  years  will 
see  this  insect  steadily  invading  new  territory  and  forcing  its  depre- 
dations upon  the  inhabitants  of  all  southern  California  and  most  of 
the  Gulf  States. 

The  present  paper  aims  to  present,  in  as  concise  a  manner  as  possi- 
ble, the  principal  results  of  five  years  of  almost  constant  observa- 
tion and  experiment  by  the  senior  author  at  Baton  Rouge,  La.,  and  in 
the  orange-growing  section  of  the  same  State,  together  with  observa- 
tions made  by  the  junior  author  at  Xew  Orleans  in  connection  with 
his  investigations  of  sugar-cane  insects. 

The  junior  author  has  prepared  in  their  entirety  the  portions  deal- 
ing with  the  "Area  of  ultimate  infestation,"  and  the  "  Relation  of  the 
ant  to  Coccidge  and  Aphididas,"  and  to  him  is  also  to  be  credited  the 
important  discovery  that  mating  of  the  queens  may  occur  within 
the  formicary  or  nest  of  the  colony.  The  remainder  of  the  paper, 
except  where  otherwise  noted,  is  compiled  from  the  notes  and  records 
of  the  senior  author. 

In  the  tedious  work  which  accompanied  the  determination  of  the 
ant's  life  history,  from  1907  to  1910,  much  assistance  was  rendered 
by  the  young  men  associated  with  the  senior  author  in  the  work  of 
the  Louisiana  State  Crop  Pest  Commission,  particularly  Messrs. 
Harper  Dean,  A.  H.  Rosenfeld,  G.  A.  Runner,  M.  S.  Dougherty, 
G.  D.  Smith,  and  R.  C.  Treherne. 

The  writers  are  under  obligations  to  Dr.  W.  M.  Wheeler,  of  the 
Bussey  Institution,  Harvard  University,  for  permission  to  use  his 
redescription  of  Iridomyrmex  humilis  and  for  his  kindness  in  reviewing 
the  paragraphs  upon  " Systematic  position"  and  "Resemblance  to 
other  ants." 

Our  thanks  are  also  due  to  Messrs.  R.  S.  Moore  and  John  Meyer, 
extensive  orange  growers  of  Louisiana,  for  their  liberal  cooperation 

9 


10  THE   ARGENTINE   ANT. 

and  assistance  in  experiments  carried  out  in  the  infested  orange 
districts. 

GENERAL  CONSIDERATIONS. 

Twenty  years  ago  the  Argentine  ant  was  first  noticed  in  New  Or- 
leans, La.,  by  Mr.  Edward  Foster,  reference  to  whose  interesting 
account  of  the  "  Introduction  of  Iridomyrmex  humilis  Mayr  into  New 
Orleans"  will  be  found  on  a  subsequent  page.  The  species  had 
doubtless  been  introduced  years  before  that  time,  but  was  gathering 
strength  and  establishing  itself  for  a  considerable  period  before  its 
numbers  became  sufficient  to  attract  attention.  Mr.  Foster  men- 
tions it  as  occurring  in  1891  in  "fair  numbers."  Since  then  it  has 
increased  from  a  few  scattered  and  apparently  insignificant  speci- 
mens to  armies  and  hordes  numbering  myriads  of  individuals.  It 
has  spread  from  a  few  blocks  on  the  water  front  of  the  Mississippi 
River  over  practically  the  entire  city,  and  has  sent  out  vast  numbers 
of  colonists  for  hundreds  of  miles  along  the  railways  and  waterways 
radiating  from  New  Orleans.  These  pioneers  have  succeeded  in 
founding  scores  of  communities  of  more  or  less  importance  in  the 
smaller  cities  and  towns.  Each  of  these  communities  is  in  turn 
furnishing  its  quota  of  migrants,  and  these  are  extending  the  affected 
territory  in  all  directions  from  the  original  source  of  infestation. 
Thus,  instead  of  the  dispersion  being  from  one  source  only,  it  is  now 
taking  place  from  hundreds  of  different  points.  From  an  unknown 
and  little  noticed  insect  this  ant  has  developed  into  one  of  the  fore- 
most household  pests  in  the  world,  and  its  ravages  affect,  directly  or 
indirect^,  the  majority  of  the  crops  grown  in  the  South.  Former 
indifference  to  its  movements  has  given  way  to  concern  at  its  approach, 
which,  in  the  orange  belt  at  least,  means  heavy  depreciation  in  the 
value  of  property. 

Continuous  study  for  several  years  has  served  to  enlighten  us  on 
most  of  the  salient  features  in  the  life  history  and  economy  of  the 
species.  A  considerable  number  of  poisons  and  repellents  have  been 
tested  and  have  given  good  results.  Methods  of  isolating,  ditching, 
and  winter-trapping  have  been  devised,  and  have  proved  their  prac- 
tical value  in  large  experiments  under  field  conditions. 

Just  how  much  territory  this  ant  will  ultimately  infest  we  can  not 
foretell  with  accuracy  from  the  data  at  present  available.  It  is 
quite  safe,  however,  to  venture  the  opinion  that  the  species  will 
eventually  spread  over  a  considerable  portion  of  the  Southern  States — 
certainly  over  all  of  the  orange  and  sugar-cane  belts,  and  perhaps  over 
all  of  the  cotton  belt.  In  California  it  is  likely  to  cover  the  territory 
corresponding  in  temperature  to  the  belts  mentioned  for  the  South, 
which  will  include  the  belts  occupied  by  oranges  and  other  tender 
fruits. 


THE   ARGENTINE   ANT.  11 

HISTORY  AND  DISTRIBUTION. 

As  stated  on  another  page,  this  species  was  first  described  by  Dr. 
Gustav  Mayr  from  specimens  collected  near  Buenos  Aires,  in  Argen- 
tina. It  is  also  included  in  the  list  of  Argentine  ants  by  Dr.  Carlos 
Berg.1  Its  occurrence  in  the  Argentine  Republic  is  therefore  unques- 
tioned, and  that  Argentina  is  its  native  home  is  also  borne  out  by  the 
fact  that  it  does  not  appear  to  be  generally  a  pest  of  importance  in  that 
country.  Dr.  F.  Lahille,  of  the  Argentine  department  of  agriculture, 
in  a  letter  to  the  senior  author,  states  that  it  "is  uncommon  in 
Buenos  Aires  and  in  Argentina  generally,  where  it  does  not  cause 
annoyance  or  trouble  of  value."  Mr.  Arthur  H.  Rosenfeld,  formerly 
associated  with  the  writers  in  entomological  work  in  Louisiana  and 
now  located  at  Tucuman,  Argentina,  writes  that  he  has  been  unable 
to  find  the  species  there.  Rev.  E.  Wasmann,  S.  J.,  states  that  this 
ant  "is  a  native  of  Brazil  and  Argentina,"  and  Rev.  Albert  Biever, 
S.  J.,  of  Loyola  College,  New  Orleans,  whose  careful  studies  of 
this  species  are  mentioned  on  other  pages,  has  corresponded  with 
various  priests  in  Brazil  and  Argentina,  with  the  result  that  he  finds 
that  this  species  is  a  serious  pest  in  parts  of  Brazil  and  evidently  in 
Argentina  also.  For  example,  in  a  letter  to  Father  Biever,  Rev.  J. 
Ferol,  S.  J.,  of  the  Colegio  del  Salvador,  Buenos  Aires,  writes: 

The  ants  {Iridomyrmex  humilis)  of  which  your  reverence  makes  mention  are  of  no 
utility  whatsoever,  but  on  the  contrary  are  voracious  and  destructive.  Of  means 
employed  to  destroy  them  the  most  effective,  according  to  information  given  me,  is 
the  use  of  an  instrument  and  ingredient  of  which  inclosed  herein  I  send  a  prospectus 
and  instructions  concerning  its  use  and  functions. 

Forel2  mentions  its  occurrence  in  collections  from  the  States  of  Sao 
Paulo  and  Rio  Grande  do  Sul,  in  Brazil.  Wheeler  3  also  mentions 
its  occurrence  in  that  country.  Dr.  Lahille  also  states  that  the 
Argentine  ant  occurs  in  Uruguay  and  is  "especially  common  in 
Mercedes  and  Montevideo,"  cities  not  far  removed  from  Buenos  Aires. 

According  to  Stoll 4  and  Wheeler 5  the  Argentine  ant,  after  its 
accidental  introduction  into  the  island  of  Madeira,  entirely  extermi- 
nated another  ant,  Plieidole  megacephala  Fab.,  which  was  itself  an 
introduced  species  that  had  exterminated  the  native  ants  before  it. 

In  1907  M.  N.  Martins6  recorded  the  occurrence  of  this  ant  in 
Lisbon  and  Oporto,  Portugal,  and  gave  a  vivid  account  of  its  ravages 
in  those  cities  and  their  environs. 

i  Enumeracion  sistematica  y  sinon^mica  de  los  Formicidos  Argentinos,  Chilenos  y  Uruguayos.    1890. 

2  Ameisen  aus  Sao  Paulo  (Brasilien),  Paraguay,  etc.  Verhandlungen  der  k.  k.  zool.-bot.  Ges.  in  Wien, 
1908. 

3  Entomological  News,  January,  1906,  p.  24. 

4  Zur  Kenntnis  der  geographischen  Verbreitung  der  Ameisen,  Mitth.  Schweiz.  Ent.  Ges.,  vol.  10,  pp. 
120-126,  1898. 

5  Ants:  Their  structure,  development,  and  behavior,  p.  154, 1910. 

6  Une  fourmi  terrible  envahissant  l'Europe  {Iridomyrmex  humilis  Mayr).  Broteria  Revista  de  Sciencias 
Naturaes,  vol.  6,  pt.  1,  pp.  101-102, 1907. 


12  THE   AKGENTINE   ANT. 

In  1908  Prof.  C.  P.  Lounsbury  recognized  this  ant  in  Cape  Town, 
South  Africa,  where  it  had  already  become  a  household  nuisance  and 
had  displayed  its  usual  role  of  attending  mealy-bugs  and  other  insects. 
The  general  belief  in  Cape  Town,  according  to  Prof.  Lounsbury,  was 
that  the  pest  had  been  introduced  through  the  medium  of  forage, 
large  quantities  of  which  were  imported  from  Argentina  during  the 
Boer  War  (1900-1902)  and  stored  in  Cape  Town. 

In  July,  1910,  the  late  Edwyn  C.  Reed,  of  Concepcion,  Chile,  in  a 
letter  to  the  senior  author,  reported  the  occurrence  of  the  species  in 
that  country  in  large  numbers. 

In  1908  ants  collected  by  Mr.  J.  Chester  Bradley,  of  the  University 
of  California,  were  identified  as  /.  fiumilis  by  Dr.  W.  M.  Wheeler. 
Immediately  following  this  discovery  Prof.  C.  W.  Woodworth,  of  the 
California  Agricultural  Experiment  Station,  visited  the  authors' 
laboratory  at  Baton  Rouge,  La.,  for  the  purpose  of  becoming  familiar 
with  the  methods  used  in  studying  the  insect  and  with  the  information 
which  had  been  gathered  concerning  it  up  to  that  time.  On  his 
return  to  California  he  published  a  brief  circular *  concerning  its 
occurrence  in  that  State. 

From  the  foregoing  it  is  readily  seen  that  during  the  past  few  years 
this  ant  has  thoroughly  established  itself,  as  a  nuisance  of  the  first 
order,  on  four  continents,  and,  owing  to  the  readiness  with  which  it  is 
disseminated  through  the  ordinary  channels  of  commerce,  there 
seems  little  reason  for  supposing  that  it  will  not  eventually  invade 
all  of  the  semitropical  countries  of  the  globe. 

INTRODUCTION    INTO   LOUISIANA. 

As  with  most  imported  species,  the  original  time  and  place  at  which 
a  foothold  was  obtained  by  the  Argentine  ant  in  Louisiana  must  be 
largely  conjectural.  However,  we  are  able  to  conjecture  with  rather 
strong  circumstantial  evidence  to  guide  us.  Not  only  does  the  tes- 
timony of  inhabitants  indicate  New  Orleans  to  be  the  original  starting 
point  of  this  species  in  the  South,  but  its  enormous  numbers  and  the 
extent  to  which  it  has  exterminated  other  species  of  Formicidae  con- 
firm the  opinion  that  it  has  been  in  New  Orleans  longer  than  else- 
where. 

Mr.  Edward  Foster,2  of  the  editorial  staff  of  the  New  Orleans 
Daily  Picayune,  has  given  us  the  earliest  record  of  its  occurrence  in 
New  Orleans.  He  noted  it  in  1891  in  St.  Charles  Avenue,  9 
squares   from  the  river  and   12  from  Canal  Street.      It   was  then 

i  The  Argentine  ant  in  California.    Cal.  Agr.  Exp.  Sta:,  Cir.  38,  August,  1908. 

2  The  introduction  of  Iridomyrmex  humilis  into  New  Orleans.    Journ.  Econ.  Ent.,  vol.  1,  No.  5.  pp. 
289-293,  October,  1908. 


HISTORY   AND   DISTRIBUTION".  13 

present  in  "fair  numbers."  At  that  date  it  was  very  scarce  in 
Audubon  Park  and  below  Canal  Street,  but  was  present  in  considerable 
numbers  between  Magazine  Street  and  the  river. 

"Five  or  six  years  later"  he  found  it  in  St.  Peters  Avenue,  near 
St.  Charles,  but  it  was  not  abundant.  This  is  about  40  squares 
north  and  west  from  the  point  on  St.  Charles  Avenue  first  referred  to 
by  Mr.  Foster. 

In  a  personal  letter  to  the  senior  author,  Mr  Foster  writes  as 
follows : 

I  have  known  the  species  since  1891.  At  that  time  it  was  a  rarity  in  Audubon  Park, 
but  was  very  common  in  the  section  immediately  above  Canal  Street.  Below  Canal 
Street  it  was  not  at  all  plentiful.  The  boundary  of  the  nuisance  then  was  virtually 
from  Magazine  Street  to  the  river.-  The  coffee  ships  from  Brazil,  I  understand,  have 
always  landed  about  where  the  wharves  are  now  situated  (on  the  river  front,  adjoining 
the  area  above  mentioned),  but  from  what  we  know  of  the  spread  of  insect  nuisances 
the  first  batch  of  immigrants  must  have  come  in  years  before  I  came  across  their 
descendants. 

Mr.  E.  S.  G.  Titus,1  quoting  Mr.  E.  Baker,  former  superintendent  of 
Audubon  Park,  states  that  in  1896  "they  extended  over  but  a  small 
area,  reaching  approximately  from  Southport  docks  to  Carrollton 
Avenue  and  from  the  river  bank  to  Poplar  Street,"  and  that  "in  1899 
they  were  first  noticed  in  Audubon  Park."  This  area,  from  Southport 
to  Carrollton  Avenue,  is  located  about  5  or  6  miles  northwest  of  the 
area  between  Magazine  Street  and  the  river,  noted  by  Foster  to  be 
well  infested  as  early  as  1891.  Mr.  Baker,  therefore,  had  not  been 
familiar  with  the  original  area  of  heavy  infestation,  but  merely  noted 
the  species  after  it  had  invaded  the  part  of  the  town  where  he  resided. 
Mr.  Titus's  information  that  the  species  was  first  noted  in  Audubon 
Park  in  1899  was  of  course  secured  from  citizens,  who  failed  to  note 
the  ant  until  it  had  reached  prodigious  numbers  in  the  same  place 
that  Foster  had  found  it  a  "rarity"  in  1891.  The  dissemination  to 
Audubon  Park  was  undoubtedly  from  the  heavily  infested  area 
between  Magazine  Street  and  the  wharves  already  referred  to. 

The  distribution  of  the  species  in  1904,  as  given  by  Mr.  Titus,2  was 
as  follows : 

Across  the  river  in  Algiers  and  adjoining  small  settlements;  at  West  End,  Spanish 
Fort,  and  Milneburg,  summer  resorts  on  Lake  Ponchartrain;  Bay  St.  Louis,  Miss.,  a 
summer  resort  between  New  Orleans  and  Mobile;  along  the  Texas  &  Pacific  Rail- 
road at  Donaldson ville,  Cheney ville,  and  Alexandria;  along  the  Southern  Pacific  at 
Thibodeaux,  Schriever,  Houma,  Berwick,  Morgan  City,  Franklin,  New  Iberia,  and 
La  Fayette,  and  at  Opelousas. 

There  is  every  reason  for  supposing  that  this  ant  was  introduced 
into  New  Orleans  by  means  of  the  coffee  ships  which  have  for  years 

»  Bui.  52,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  p.  79,  1905.  2  Ibid.,  p.  82. 


14 


THE    ARGENTINE    A  XT. 


passed  back  and  foTth  between  that  city  and  Brazilian  ports.  This 
view  is  supported  by  the  fact  that  large  numbers  of  the  ants  were 
first  noticed  in  the  vicinity  of  the  wharves  where  these  ships  unloaded 
their  cargoes  and  also  by  the  fact  that  these  ships  have  been  the  only 
means  of  regular  communication  between  Xew  Orleans  and  the 
countries  in  which  the  ant  is  indigenous.  That  this  and  other  species 
of  ants  are  actually  transported  on  ocean-going  vessels  has  been  fre- 
quently observed.  Thus  in  July,  1911,  the  senior  author,  while  a 
passenger  on  one  of  the  largest  coastwise  vessels  between  New  Or- 
leans and  Xew  York,  found  colonies  of  this  same  ant  occupying  pro- 
tected situations  in  the  woodwork  of  the  steamer.  Dr.  W.  M.  "Wheeler 
also  writes  us  that  while  returning  from  Guatemala  aboard  a  fruit 


Fig.  1.— Map  of  Alabama,  Mississippi,  and  Louisiana,  showing  counties  in  the  Southern  States  which  are 
infested  by  the  Argentine  ant,  according  to  the  authors'  records.    (Original.) 

steamer  in  January,  1912,  he  found  it  infested  with  another  common 
ant,  Prenolepis  longicornis  Fab. 


PRESENT    DISTRIBUTION    IN    THE    SOUTHERN    STATES. 

The  area  in  the  Southern  States  within  which  the  Argentine  ant 
is  known  to  occur  at  present  extends  from  Montgomery,  Ala.,  to 
Lake  Charles,  La.,  a  distance  of  about  380  miles  east  and  west;  and 
from  Delta,  La.,  to  the  mouth  of  the  Mississippi  River,  a  distance  of 
about  250  miles  north  and  south.  (See  fig.  1.)  This  section  is  not 
uniformly  infested,  but  contains  a  great  number  of  infested  areas  of 
more  or  less  importance,  ranging  in  size  from  many  square  miles  of 


HISTORY    AND   DISTRIBUTION.  15 

occupied  territory,  as  illustrated  by  the  infestation  at  New  Orleans, 
to  areas  where  the  ants  are  so  scarce  that  one  not  accustomed  to  their 
habits  would  fail  to  discover  them.  The  latter  condition  prevails  at 
present  in  Mobile,  Ala.  The  only  places  remote  from  railroads 
where  they  have  been  discovered  are  upon  the  banks  of  the  Missis- 
sippi River  below  infested  localities.  Their  presence  in  such  loca- 
tions is  easily  accounted  for  by  supposing  that  they  have  been  carried 
thither  on  driftwood,  which,  carrying  numbers  of  ants  from  infested 
places  farther  up  the  stream,  has  become  stranded  on  the  river  banks, 
thus  establishing  new  foci.  In  all  other  cases  the  infested  territory 
is  on  a  railroad,  and  usually  on  a  main  line  running  out  from  New 
Orleans.  For  example,  nearly  every  town  along  the  Southern  Pa- 
cific Railway  between  New  Orleans  and  Lake  Charles  is  infested,  and 
the  same  statement  applies  to  points  on  the  Louisville  &  Nashville 
Railroad  between  New  Orleans  and  Mobile. 

OCCURRENCE    AND   DISTRIBUTION    IN    CALIFORNIA. 

The  first  specimens  of  the  Argentine  ant  observed  in  California 
were  collected  in  1907  by  Mr.  J.  Chester  Bradley,  at  that  time  an 
assistant  in  the  entomological  department  of  the  University  of  Cal- 
ifornia. The  identity  of  the  specimens  was  not  established  until 
1908,  when  Dr.  W.  M.  "Wheeler  found  them  to  be  Iridomyrmex  Jiumilis 
Mayr. 

As  soon  as  the  dangerous  nature  of  the  pest  was  known,  Prof.  C.  W. 
Woodworth  took  steps  to  make  a  study  of  the  species  along  the  same 
lines  as  was  being  conducted  in  Louisiana  at  that  time,  and  as  a  result 
of  his  preliminary  work  he  issued  a  warning  circular  x  to  the  public 
in  August,  1908.  In  this  circular  he  gave  a  brief  outline  of  the 
habits  of  the  ant  and  reported  the  following  localities  as  infested: 
In  the  central  portion  of  the  State,  East  Oakland,  Alameda,  San 
Francisco,  San  Jose,  Cupertino,  and  a  point  near  Campbell;  in  the 
southern  part  of  the  State,  Los  Angeles,  Azusa,  and  Upland. 

In  1910  Prof.  Woodworth  published  another  small  bulletin  2  giving 
the  results  of  his  two  years'  study  of  the  insect.  In  this  paper  the 
infested  territory  was  more  clearly  defined,  and  was  estimated  as 
consisting  of  a  total  area  of  5,000  acres.  About  twice  the  area  was 
reported  infested  in  1910  as  in  1908,  owing  to  the  discovery  of  a  few 
new  colonies  and  the  natural  spread  of  the  ones  first  discovered. 

Our  information  as  to  the  extent  of  the  infested  area  in  California 
(see  fig.  2)  has  been  obtained  principally  through  the  kind  offices  of 
Mr.  Ralph  Benton,  of  the  California  Agricultural  Experiment  Station, 
and  Mr.  P.  E.  Smith,  of  Santa  Paula,  Cal.,  as  well  as  from  the  publi- 

i  The  Argentine  ant  in  California.    Cal.  Exp.  Sta.  Cir.  38,  Berkeley,  Cal.,  August,  1908. 
2  The  control  of  the  Argentine  ant.    Cal.  Exp.  Sta.  Bui.  207,  Berkeley,  Cal.,  October,  1910. 


16 


THE   ARGENTINE  ANT. 


cations  by  Prof.  C.  W.  Woodworth,  already  referred  to.  All  of  these 
persons  agree  that  the  following  California  points  are  infested:  Ala- 
meda, Azusa,  Berkeley,  Byron  Hot  Springs,  Campbell,  College  Park, 
Cupertino,  Fruitvale,  Los  Angeles,  Melrose,  Oakland,  Riverside,  San 
Francisco,  San  Jose,  Stockton,  and  Upland. 


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Fig.  2.— Distribution  of  the  Argentine  ant  in  California.    From  data  furnished  by  Messrs.  Ralph  Benton 
and  P.  E.  Smith.    (Original.) 

AREA    OF   ULTIMATE    INFESTATION. 


Up  to  the  present  we  have  no  exact  data  to  indicate  the  final  limits 
of  the  area  which  may  become  infested  by  these  ants.  They  appar- 
ently thrive  as  well  at  Delta,  La.,  at  an  elevation  of  87  feet,  as  they 
do  near  the  mouth  of  the  Mississippi  River,  300  miles  to  the  south 
and  almost  at  sea  level.     They  seem  to  be  little  or  not  at  all  affected 


HISTORY  AND   DISTRIBUTION.  17 

by  the  variation  in  the  amount  of  precipitation  annually  as  between 
different  localities,  for  they  seem  to  flourish  as  well  at  San  Jose  and 
Los  Angeles,  Cal.,  with  average  annual  rainfalls  of  14.8  and  15.6 
inches,  respectively,  as  they  do  at  New  Orleans,  La.,  where  the  aver- 
age annual  rainfall  is  57.6  inches.  The  range  of  temperature  to 
which  they  have  adapted  themselves  at  different  points  does  not 
vary  so  greatly,  but  is  nevertheless  considerable.  They  have  suc- 
ceeded in  establishing  themselves  at  San  Francisco,  Cal.,  where  the 
mean  annual  surface  temperature  is  56°  F.,  or  13°  cooler  than  the 
mean  annual  surface  temperature  at  New  Orleans,  La. 

If  we  assume  that  the  Argentine  ant  is  unable  to  persist  in  local- 
ities where  the  mean  annual  temperature  is  below  55°,  we  will  find 
that  the  isotherm  of  this  temperature  extends  almost  up  to  Columbus, 
Ohio,  and  past  St.  Louis,  Mo.,  and  will  include  over  one- third  of  the 
United  States,  or  more  than  1,000,000  square  miles.  It  is  very 
unlikely,  however,  that  this  neotropical  species  will  be  able  to  endure 
the  cold  winters  in  the  northern  parts  of  this  area.  It  will  probably 
be  more  nearly  correct  to  assume  that  its  advance  will  be  checked 
when  it  reaches  the  minimum  isotherm  of  zero,  or,  in  other  words, 
where  the  thermometer  drops  to  zero  or  below  during  the  average 
winter.  On  constructing  this  isotherm  we  find  that  we  have  the 
following  area  within  the  United  States  liable  in  the  course  of  time 
to  infestation  by  the  Argentine  ant : 

Starting  at  the  Atlantic  coast  line;  one-half  of  North  Carolina, 
one-half  of  South  Carolina,  one-half  of  Georgia,  Florida,  a  portion  of 
Alabama,  one-third  of  Mississippi,  most  of  Louisiana,  all  of  lower 
Texas,  a  corner  of  New  Mexico,  one-half  of  Arizona,  a  little  of  Ne- 
vada, practically  all  of  California,  and  a  coastal  strip  through  Oregon 
and  Washington.  This  would  extend  the  infestation  into  fourteen 
States,  more  or  less,  and  is  undoubtedly  a  very  conservative  predic- 
tion, as  already  the  ant  is  established  at  one  point,  Delta,  La.,  which 
is  above  this  line. 

In  spite  of  these  considerations  we  are  still  in  the  dark  as  to  the 
altitudes. at  which  this  insect  will  thrive,  and  it  may  be  found  later 
that  altitude  will  severely  limit  the  distribution  of  this  species,  as  it 
does  that  of  many  other  insects.  Table  I  gives  the  elevation  and 
climatological  data  for  a  number  of  infested  points  in  the  United 
States,  and  from  this  table  it  will  be  noted  that  the  elevation  of 
points  now  infested  varies  from  sea  level  to  338  feet. 

The  climatological  data  given  in  Table  I  are  taken  from  Bulletin  Q, 
Weather  Bureau  of  the  United  States  Department  of  Agriculture, 
1906,  entitled  " Climatology  of  the  United  States,"  by  Alfred  Judson 
Henry. 

75508°— Bull.  122—13 2 


18 


THE   ARGEXTIXE   ANT. 


Table  I. — Data  concerning  various  towns  infested  with  the  Argentine  ant. 


Name  of  town.                 E^ 
■ 

Mean 
annual 
temper- 
ature. 

Absolute 
maximum 
temper- 
ature. 

Summer 

maximum, 

mean. 

Absolute 
minimum 
temper- 
ature. 

Winter 

minimum, 

mean. 

Mean 
annual 
precipita- 
tion. 

Montgomery.  Ala 

Mobile.  Ala. 

Feet. 
196 
11 

°F. 
66 
67 
65 
64 
67 
67 
66 
67 

67 
68 
69 
60 
56 
58 
62 

°F. 
107 
102 
101 
104 
103 
100 
109 
103 

0) 

103 
101 
102 
108 
100 
104 
109 

°F. 
90 
89 
90 
89 
92 
88 
92 
90 

(') 
91 
89 
88 
87 
65 

•F. 

-  5 

-  1 

-  1 

-  6 

-  1 
1 
2 
2 

(') 

3 
6 
7 
19 
29 
18 
28 

°F. 
40 
45 
42 
38 
40 
43 
39 
42 

41 

45 
48 
40 
46 

Inches. 
50.8 
62  1 

229 
338 
154 

24 

62 
87 
22 
15 
8 
29 

53  8 

53  4 

Hattiesburg,  Miss 

48  1 

Biloxi.  Miss 

61.3 
54  9 

Baton  Rouge,  La 

54.6 

Delta,  La 

53.3 
53.7 

Lake  Charles,  La 

New  Iberia.  La 

New  Orleans,  La 

57.6 
19  9 

San  Francisco,  Cal 

San  Jose.  Cal 

28 
95 

287 

22.5 
14  8 

82 

45 

15  6 

1  Records  not  available. 

Note. — "  Summer  maximum,  mean  "=the  average  of  the  total  maximums  for  June, 
July,  and  August.  "Winter  minimum,  mean  "=the  average  of  the  total  minimums 
for  December,  January,  and  February. 


COMMON    XAME. 

The  name  " Argentine  ant"  was  first  used  by  the  senior  author  for 
this  species  in  1908,  when  the  public  was  on  the  point  of  accepting 
the  name  "New  Orleans  ant."  The  permanent  use  of  the  latter 
name  would  manifestly  have  been  unjust  to  the  Crescent  City,  for 
that  city  was  in  no  way  responsible  for  the  introduction  of  the  pest. 
As  stated  on  preceding  pages,  this  ant  was  originally  described  from 
specimens  collected  in  Argentina,  South  America,  and  up  to  the 
present  time  we  have  no  reasons  for  not  believing  that  this  is  one,  at 
least,  of  the  countries  in  which  this  ant  is  native.  The  naming  of 
this  ant  after  the  country  from  which  it  was  first  described  is  by  no 
means  without  precedent.  Many  other  common  insects,  such  as 
the  San  Jose  scale,  American  cockroach,  Colorado  potato  beetle, 
Mexican  cotton-boll  weevil,  etc.,  have  received  their  popular  names 
in  the  same  manner. 

Various  common  names  have  been  suggested  from  time  to  time, 
among  them  "crazy  ant,"  "tropical  ant,"  "pernicious  ant,"  etc., 
but  all  have  the  disadvantage  of  being  as  applicable  to  other  species 
as  to  Iridomyrmex  hurnilis  and  none  of  them  is  distinctive. 

The  term  "Argentine  ant"  has  been  readily  accepted,  alike  by 
entomologists  and  the  press,  is  concise,  and  not  likely  to  be  confused 
with  similar  names;  hence  we  believe  it  to  be  as  good  a  name  as  can 
be  adopted. 


THE   ARGENTINE   ANT.  19 

MEANS  OF  DISPERSION. 
NATURAL    SPREAD. 

Under  strictly  natural  conditions,  the  rate  of  dispersion  of  Argen- 
tine ants  is  very  slow.  Owing  to  their  intensely  social  habits  they 
spread  but  slowly  from  a  locality  until  the  number  present  becomes 
excessive  for  the  food  supply  or  unless  adverse  conditions,  such  as 
flooding,  occur  which  compel  them  to  seek  fresh  locations.  They 
will  then  spread  in  all  directions,  but  will  go  little  farther  than  is 
necessary  to  give  them  sufficient  foraging  area  to  insure  the  food 
required.  However,  if  a  large  food  supply  is  discovered  at  a  con- 
siderable distance  from  the  colony,  a  heavy  trail  of  workers  will 
soon  be  formed  between  the  food  and  the  nest,  composed  of  many 
thousands  of  tiny  insects,  each  busy  carrying  a  load  of  the  coveted 
material  back  to  the  nest  or  going  out  for  another  load.  Sometimes 
they  will  construct  a  new  nest  in  the  neighborhood  of  the  food  sup- 
ply, and  to  this  they  will  transport  a  number  of  pupae,  larvae,  and 
eggs  from  the  parent  nest.  In  the  course  of  a  day  or  so  this  new 
colony  mil  be  thoroughly  established,  with  a  full  supply  of  queens, 
workers,  and  immature  stages,  and  will  then  be  capable  of  supporting 
itself  and  increasing  in  numbers  without  assistance  from  the  parent 
nest. 

Under  normal  conditions  it  is  likely  that  the  rate  of  spread  does 
not  amount  to  more  than  a  few  hundred  yards  each  year.  When 
food  is  plentiful,  a  well-traveled  road  or  a  paved  street  may  restrict 
the  spread  for  a  considerable  period,  but  when  any  much-desired 
food  supply,  such  as  the  excretions  of  aphides  or  scale  insects,  is  to  be 
reached,  nothing  short  of  running  water  proves  an  effective  barrier. 

FLIGHT. 

It  is  possible,  but  scarcely  probable,  that  the  queens  may  aid  the 
natural  dispersion  by  means  of  flight,  but  there  are  several  reasons 
why  this  is  doubtful.  One  of  them  is  that  the  flight  itself  is  a  very 
uncertain  event,  as  during  the  five  years  that  these  ants  have  been 
studied  in  Louisiana  only  one  general  flight  has  been  observed.  It 
has  been  established  that  the  young  queens  can  mate  in  the  nest 
without  taking  a  marriage  flight  at  all,  and  apparently  this  is  what 
usually  takes  place.  Even  should  a  fertilized  winged  queen  fly  or 
be  transported  by  the  wind  to  any  considerable  distance  from  the 
ant-infested  territory,  it  is  very  doubtful  whether  any  eggs  she  might 
lay  would  ever  hatch.  The  queen  has  never  been  observed  assisting 
in  the  slightest  degree  with  the  rearing  of  the  young  in  the  nest,  nor 
have  we  succeeded  in  getting  eggs  to  hatch  when  they  were  not 
cared  for  by  the  workers.  As  the  workers  are  never  winged,  the 
queen  would  necessarily  be  alone,   and  it  would  be  very  unlikely 


20  THE   ARGENTINE    ANT. 

that  the  queen  would  develop  the  instinct  of  attending  to  and  caring 
for  the  eggs,  larvae,  and  pupae  in  succession  for  several  months. 
Also,  the  queens  are  quite  helpless  and  appear  to  be  entirely  incapa- 
ble of  defending  themselves  against  other  insects.  The  writer  has 
observed  a  queen  ant  being  captured  and  bound  by  a  minute  spider, 
considerably  smaller  in  size  than  her  own  head,  without  making 
the  least  attempt  to  struggle.  It  therefore  seems  improbable  that  a 
defenceless  queen  could  maintain  herself  in  a  hostile  country  for 
several  months  without  the  assistance  of  workers. 

Furthermore,  we  have  several  times  kept  Argentine  ant  queens 
isolated  in  small  nests,  sometimes  singly  and  sometimes  in  groups, 
but  have  never  yet  succeeded  in  hatching  eggs  in  these  nests,  or  in 
rearing  larvae  to  the  adult  stage. 

The  fact  that  ditches  of  running  water  have  proven  sufficient  bar- 
riers to  prevent  the  spread  of  the  species  in  orange  groves  appears  to 
disprove  the  theory  that  queens  returning  from  the  nuptial  flight  can, 
without  the  assistance  of  workers,  establish  new  colonies. 

DISPERSION   BY   STREAMS. 

As  previously  mentioned,  driftwood  is  probably  the  most  important 
agency  in  the  natural  dispersion  of  the  Argentine  ant.  Along  the 
Mississippi  River,  below  the  infested  territory,  we  find  a  considerable 
number  of  larger  or  smaller  colonies  of  the  ants,  and  in  places  the 
batture  *  will  be  infested  for  miles,  with  practically  no  ants  inside  the 
levee.  This  can  only  be  accounted  for  by  ants  floating  down  the 
river  upon  driftwood  from  infested  localities.  The  river  banks  are 
covered  with  logs,  more  or  less  rotten,  which  have  stranded  during 
high  water.  In  the  infested  territory  these  logs  are  found  full  of 
ants  in  ail  stages  in  enormous  numbers.  During  high  water  some  of 
these  logs  drift  and  lodge  alternately,  gradually  working  down  the 
river,  and  distributing  colonies  in  their  wake. 

The  writer  has  several  times  seen  complete  colonies  of  ants  on  a 
floating  log,  unable  to  escape.  All  that  was  required  was  a  little 
further  rise  of  the  water  to  start  them  down  the  river,  with  their 
cargoes  of  ants. 

ARTIFICIAL   DISSEMINATION. 

Unquestionably  the  main  distributing  agent  of  the  Argentine  ant 
is  man  himself,  by  means  of  railway  trains,  boats,  and  other  vehicles 
which  he  controls  and  utilizes  in  the  transportation  of  freight  and 
commodities  of  all  kinds.  The  ants  must  necessarily  have  been  intro- 
duced to  this  country  by  means  of  ships,  and  railways  have  been  the 

1  The  "batture"  is  that  land  lying  between  the  true  bank  of  the  river  and  the  levee.  The  batture  is 
subject  to  overflow  during  high  water,  is  ordinarily  not  cultivated,  and  is  frequently  overgrown  with  wil- 
lows. The  batture  is  said  to  be  "outside"  the  levee,  while  land  protected  by  the  levee  from  high  water  is 
said  to  be  "inside"  the  levee. 


MEANS   OF   DISPERSION.  21 

principal  means  of  dissemination  since  they  succeeded  in  establishing 
themselves.  This  is  evident,  as  all  the  centers  of  infestation  so  far 
discovered,  with  the  exception  of  those  down  the  Mississippi  River, 
the  presence  of  which  has  just  been  explained,  are  located  upon 
railway  lines;  in  the  Southern  States,  upon  mam  lines  running  out 
of  Xew  Orleans. 

The  ants  are  easily  transported  in  packing  and  freight  of  various 
kinds.  Large  numbers  of  potted  plants  are  shipped  out  of  New 
Orleans  to  the  surrounding  country,  and  in  many  cases  complete 
colonies  of  ants  are  sent  with  them  in  the  soil  surrounding  the  roots. 
Boxes  and  barrels  of  groceries,  packing  placed  around  fragile  material 
to  prevent  breakage,  and  shipments  of  household  goods  may  all 
contain  queens  and  workers  when  shipped  from  infested  points.  The 
writer  has  observed  a  queen  and  many  workers  inside  an  empty 
passenger  coach,  which  had  been  standing  on  the  track  for  several 
hours  during  a  rainstorm. 

The  danger  of  promiscuous  infestation  is  somewhat  lessened  by  the 
fact  that  it  is  necessary  for  a  queen  ant  to  be  transported  with  the  workers 
in  order  that  a  new  colony  may  be  founded.  In  a  large  series  of  ex- 
periments conducted  to  determine  this  point  we  have  never  yet  found 
any  indication  that  the  workers  were  able  to  produce  eggs,  or  to 
reproduce  their  kind  in  any  manner.  Consequently  large  numbers 
of  workers  may  be  scattered  broadcast  over  uninfested  territory  and, 
though  they  may  live  for  a  considerable  time,  they  will  ultimately 
die  out  if  a  queen  is  not  present.  It  is  probably  due  to  this  fact  that 
these  ants  have  not  infested  a  great  deal  more  territory  than  they 
have  during  the  past  10  years,  as  it  is  a  certainty  that  thousands 
of  workers  are  being  continually  shipped  from  infested  territory  into 
uninfested  localities.  At  the  same  time  the  danger  that  fertile 
queens  will  be  transported  is  considerable,  for  we  have  frequently 
found  dealated  queens  foraging  with  the  workers.  The  fertile  queens 
will  "take  up  "  with  any  workers  of  the  species,  and  it  is  only  necessary 
for  a  queen  and  workers  to  be  present  in  a  new  locality  in  order  to 
start  a  self-perpetuating  infestation. 

Steamboats  plying  up  and  down  rivers,  carrying  freight  from 
infested  points,  are  responsible  for  spreading  great  numbers  of  ants. 
For  example,  between  New  Orleans  and  Baton  Rouge,  La.,  there  are 
over  a  hundred  steamboat  landings.  These  are  nearly  all  infested 
by  the  Argentine  ant,  and  probably  the  insects  were  first  introduced 
in  the  freight  shipped  direct  to  these  points  from  New  Orleans  or 
Baton  Rouge.  Many  of  the  river  steamboats  are  so  heavily  infested 
by  permanent  colonies  of  this  ant  that  the  workers  are  almost  as  much 
of  a  nuisance  in  the  cook's  galley  as  they  are  in  culinary  establishments 
on  shore. 


22  THE   ARGENTINE  ANT. 

ECONOMIC  IMPORTANCE. 

Up  to  the  present  time  the  Argentine  ant  has  attracted  most  atten- 
tion as  a  household  pest.  Particularly  during  rainy  weather,  when 
honeydew  is  scarce,  the  ants  invade  houses  in  myriads  and  drive  the 
housekeepers  almost  to  distraction.  Nearly  everything  which  is 
edible  for  human  beings  is  attractive  to  them,  and  ceaseless  attention 
and  strenuous  effort  are  necessary  to  keep  them  out  of  pantry  and 
kitchen.  The  use  of  poisons  and  repellents  must  be  continuous; 
if  there  has  been  a  little  carelessness  in  this  regard  the  foodstuffs 
become  filled  with  countless  numbers  of  ants  in  a  very  short  time. 

Among  the  foodstuffs  most  eagerly  sought  may  be  mentioned 
honey,  sirups,  sugar,  candy,  cakes,  cookies,  jams,  marmalades,  pre- 
serves, fruit  juices,  cream,  olive  oil,  lard,  egg  (either  raw  or  cooked), 
fish  (either  fresh  or  canned),  and  various  raw  meats,  such  as  chicken, 
veal,  mutton,  pork,  beef,  etc.  Corn  meal  is  sometimes  the  object 
of  attack  and  wheat  flour  to  a  slight  extent. 

Aside  from  their  invasions  of  food  the  ants  are  household  nuisances 
generally.  No  corner  or  nook  is  safe  from  their  explorations  and  the 
discovery  of  something  edible  is  quickly  heralded  in  the  nest,  whence 
come  thousands  of  workers  to  carry  away  the  plunder.  In  heavily 
infested  sections  it  is  often  necessary  to  place  bedposts  upon  panes  of 
glass  coated  with  vaseline  or  other  repellent  in  order  that  the  occu- 
pant may  sleep  in  peace.  To  have  ants  running  all  over  one's  person 
is  disagreeable  enough,  but  what  is  more  serious,  they  will  not  hesitate 
to  attack  any  part  of  the  body  where  skin  or  membranes  are  tender 
enough  to  be  pierced  by  their  mandibles. 

Authentic  cases  are  on  record  where  it  has  been  necessary  to  take 
babes  from  their  cradles  and  repeatedly  immerse  them  in  water  to 
rid  them  of  the  ants  which  crawled  by  hundreds  over  their  bodies 
and  into  their  mouths  and  nostrils.  We  have  even  received  reports 
of  infants  being  killed  by  the  ants,  but  such  reports  we  have  not 
verified.  Such  a  thing  is  not,  however,  outside  the  realm  of 
possibility. 

In  groceries  and  stores  they  are  kept  out  of  sirups,  sugar,  molasses, 
and  like  products  only  with  great  difficulty.  In  restaurants  and 
confectionery  shops  the  closest  vigilance  is  required  to  keep  the  ants 
out  of  the  cakes,  candies,  ice  cream,  fruits,  etc.,  as  well  as  out  of  ice 
boxes,  refrigerators,1  show  cases,  and  windows.  Meat  in  butchers' 
shops  is  also  a  great  attraction,  and  if  left  unprotected  for  even  a 
short  time  thousands  of  ants  will  be  swarming  over  it. 

In  nurseries  and  among  ornamental  plants  the  ants  foster  and 
protect  countless  thousands  of  scale  insects  and  plant  lice,  the  excre- 
tions of  which  furnish  the  choicest  delicacy  with  which  the  ants 

1  The  temperature  of  the  ordinary  refrigerator  is  not  low  enough  to  deter  the  ants  in  their  foraging. 


ECONOMIC    IMPORTANCE.  23 

regale  themselves.  This  protective  care  results  in  rapid  increase  of 
these  insects,  with  resultant  damage  to  the  plants  infested.  In 
florists'  establishments  the  ants  sometimes  sever  the  petals  of  cut 
flowers  in  then  search  for  nectar. 

Visits  to  flowers  of  various  kinds  seem  a  natural  habit,  and  when 
the  ants  do  not  find  the  nectar  readily  available  they  quickly  cut 
then  way  to  it  in  all  cases  where  the  plant  tissue  is  tender  enough 
to  permit  of  it.  In  then  attacks  upon  orange  blossoms  they  are 
particularly  severe,  as  they  sometimes  eat  their  way  into  the  fruit 
buds  even  before  the  latter  are  fully  open.  The  workers  have  also 
been  noticed  regularly  visiting  the  extra-floral  nectaries  of  cotton 
and  other  plants. 

To  truck  growers  the  ants  are  very  troublesome,  owing  to  the 
manner  hi  which  they  remove  certain  garden  seeds  before  they  have 
sprouted.  Lettuce  seed  is  especially  subject  to  this  attack,  and  in 
infested  districts  the  rows  of  lettuce  seed  are  covered  with  corn  meal, 
which  is  also  attractive  to  the  ants.  By  the  time  the  ants  have 
removed  the  meal  the  lettuce  seeds  will  have  sprouted,  The  ants 
also  assiduously  attend  plant  lice  on  a  number  of  vegetables,  making 
the  latter  unpleasant  to  handle.  Cabbage  heads  are  often  found 
through  which  plant  lice  and  ants  are  completely  distributed,  the 
cabbage  leaves  merely  serving  as  divisions  between  layers  of  the 
insects. 

In  the  sugar-cane  fields  the  ant  again  comes  to  the  front,  owing 
to  its  fondness  for  the  excretions  of  the  sugar-cane  mealy-bug, 
Pseudococcus  calceolarix.  (See  figs.  3,  4.)  In  order  to  protect 
these  insects  from  storms  and  enemies,  the  ants  build  protective 
coverings  and  shelters  over  them  and  attend  them  constantly.  (See 
fig.  5.)  As  the  result  of  these  attentions  the  mealy-bugs  thrive  in 
numbers  and  destructiveness  to  an  extent  which  is  impossible  where 
the  ants  are  not  present.  Luckily  the  territory  infested  by  the 
mealy-bug  is  as  yet  very  restricted,  but  this  insect  threatens  to 
become  a  serious  problem  hi  the  future,  owing  to  the  manner  hi 
which  it  destroys  the  eyes  of  "seed  cane"  after  it  is  planted,  prevent- 
ing sprouting  and  thus  injuring  the  stand.  The  vacant  rows  in  a 
field  of  cane,  due  to  this  injury,  are  shown  hi  figure  3.  The  control  of 
this  mealy-bug  therefore  resolves  itself  into  the  problem  of  controlling 
the  ant. 

In  cornfields  it  can  be  easily  noticed  that  aphides  are  several  times 
as  numerous,  and  are  also  more  generally  distributed,  hi  districts 
infested  by  the  Argentine  ant  than  in  the  noninfested  districts.  The 
ants  are  also  found  in  great  numbers  attending  plant  lice  upon  cotton 
plants,  and  in  a  cotton  field  at  Baton  Rouge,  where  these  ants  were 
very  numerous,  it  was  noticed  that  the  cotton  aphides  remained 


24 


THE   ARGENTINE   ANT. 


abundant  throughout  the  entire  summer  and  autumn,  whereas 
during  these  portions  of  the  year  they  are  normally  almost  absent. 
It  is  in  the  orange  groves  of  southern  Louisiana,  however,  that 
this  ant  has  probably  inflicted  the  most  serious  injur}'.  This  injur}' 
is  discussed  at  length  on  a  subsequent  page.  Suffice  it  to  say  that 
at  present  the  Argentine  ant  is  there  regarded  as  the  most  serious 
insect  problem,  owing  to  the  marked  increase  of  scale  insects  which 
follows  its  introduction  and  spread.  The  value  of  land  in  that 
section  depends  to  a  considerable  extent  upon  the  presence  or  absence 
of  the  Argentine  ant.  The  ant  also  does  considerable  damage  to  the 
fig  crop  by  boring  through  the  ripened  fruit  or  entering  the  calyx  end 
of  the  ripening  fig  and  tunneling  the  interior.     It  also  assists  in  the 


Fig.  3.— Injury  to  the  stand  of  sugar  cane  by  the  sugar-cane  mealy-bug  (Pseudococcm  calceolarise).  which 
is  attended  by  the  Argentine  ant.    (Original.) 

increase  of  the  destructive  mealy-bug,  Pseudococcus  citri,  which 
injures  figs  to  a  considerable  extent. 

The  ant  is  a  veritable  plague  among  honey  bees,  and  beekeeping 
on  any  considerable  scale  is  invariably  abandoned  after  the  ants 
become  numerous. 

In  the  poultry  yard  this  ant  is  a  pest  that  must  be  reckoned  with. 
The  ants  find  the  nests  of  sitting  hens  particularly  attractive,  and  if 
perchance  an  egg  be  broken  the  ants  will  come  in  such  numbers  that 
the  fowl  will  abandon  her  nest.  The  blood  and  fluids  from  partially 
incubated  embryos  are  particularly  liked  by  the  ants,  and  when  the 
eggs  are  hatching  the  workers  swarm  over  the  young  chicks  in  such 


ECONOMIC   IMPORTANCE. 


25 


numbers  as  to  cause  their  death.  Repellents  which  can  be  adapted 
to  such  a  case  are  rare,  even  pyrethrum  powder  being  practically 
ineffective.  The  only  substance  we  have  found  which  would  at  all 
protect  the  sitting  hens  is  zenoleum  powder,  liberally  sprinkled 
in  the  nest  and  among  the  hen's  feathers  from  time  to  time 
during  the  brooding  period.  The  nests  of  many  birds  are 
frequented  by  the  ants  in  the  same  way,  and  the  number  of 
young  birds  destroyed  in  this  manner  must  be  considerable.  The 
ubiquitous  English  spar- 
row, however,  seems  to 
flourish,  as  ever,  in  spite 
of  the  ants. 

Another  form  of  injury, 
though  indirect,  is  due  to 
the  antagonism  which  ex- 
ists between  the  Argentine 
ant  and  other  species  of 
ants,  and  which  terminates 
only  with  annihilation  of 
the  native  species.  As  the 
result  of  this,  beneficial 
species  of  ants  (such  as  the 
"  fire  ant,"  Solenopsisgemi- 
nata,  which  destroys  a  con- 
siderable number  of  boll 
weevils  in  their  immature 
stages)  are  exterminated, 
and  their  place  is  taken  by 
the  infinitely  more  trouble- 
some Argentine  ant. 

It  may  presently  be 
found  that  the  Argentine 
ant  is  an  important  agent 
in  the  spread  of  disease. 

The  Workers  Congregate  in  FlG-  4.— Sugar-cane  mealy-bugs  on  sugar  cane.    (Original.) 

great  numbers  around  garbage  pails,  privies,  etc.,  and  are  frequently 
very  hard  to  keep  out  of  sick  rooms,  the  odors  seeming  to  attract  them. 
They  have  been  watched  busily  carrying  away  the  sputum  of  a  negro 
who  was  suffering  from  tuberculosis.  There  are  many  ways  in 
which  it  is  possible  for  these  ants  to  assist  in  the  distribution  of 
various  disease-producing  organisms. 

Rarely  the  activities  of  this  ant  take  on  a  beneficial  aspect.  Father 
Biever  states  that  they  have  in  many  cases  completely  exterminated 
the  bedbugs  in  the  hovels  and  tenements  occupied  by  poor  people  in 
the  city  of  New  Orleans.     The  same  authority  several  years  ago 


F 

26 


THE   ARGENTINE  ANT. 


called  attention  to  the  scarcity  of  the  common  "chiggers"  or  so-called 
"red  bugs"  in  parks  and  yards  heavily  infested  by  the  ant,  and  this 
latter  observation  has  been  verified  by  the  junior  author  in  the  case 
of  Audubon  Park,  New  Orleans.  At  Baton  Rouge,  however,  the 
senior  author  found  the  "chiggers"  very  abundant  in  premises  heav- 
ily infested  by  the  ants.  The  manner  in  which  these  ants  destroy 
the  sorghum  midge  is  described  on  following  pages. 

SYSTEMATIC  POSITION. 

According  to  the  classification  adopted  by  Dr.  W.  M.  Wheeler,1 
the  Argentine  ant  is  placed  in  the  subfamily  Dolichoclerina?,  which 


Fig.  5.— Covering  constructed  by  the  Argentine  ant  to  protect  the  mealy-bugs.    (Original.) 

is  one  of  the  five  main  subdivisions  of  the  family  Formicidse. 


The 


Dolichoderinse  are  characterized  by  the  cloacal  orifice  being  slit- 
shaped  and  ventrally  located  instead  of  being  circular  and  termi- 
nally located,  as  in  the  camponotine  ants,  by  vestigial  sting,  by 
single-segmented  abdominal  pedicel,  by  a  much  shortened  or  bell- 
shaped  gizzard  (proventriculus),  by  the  pupae  being  always  naked 
(not  inclosed  in  cocoons),  and  usually  by  anal  glands  which  produce 
a  secretion  having  a  very  offensive  odor.  In  the  case  of  the  Argen- 
tine ant,  however,  this  odor  is  entirely  lacking. 

1  "Ants,  their  structure,  development,  and  behavior,"  1910. 


SYSTEMATIC   POSITION.  27 

The  subfamily  Dolichoderinse  contains  six  North  American  genera : 
Dolichoderus  (Hypoclinea),  Forelius,  Tapinoma,  Dorymyrmex,  Lio- 
metopum,  and  Iridomyrmex.  Iridomyrmex  is  essentially  tropical  in 
its  distribution  and  only  two  species  are  known  to  occur  in  the  United 
States,1  the  native  Iridomyrmex  analis  Ern.  Andre,  common  in  cotton 
fields  of  the  South,  and  the  introduced  species,  Iridomyrmex  Jiumilis 
Mayr,  or  Argentine  ant. 

DESCRIPTION    OF   THE    SPECIES. 

Three  forms  only  of  the  adults  are  found  in  the  colonies  of  the 
Argentine  ant,  the  females  or  queens,  the  workers,  and  the  males. 
(See  fig.  6.)  Major  and  minor  workers  do  not  occur,  and  no  workers 
seem  to  act  in  the  capacity  of  soldiers  or  scouts  more  than  others. 
As  previously  noted,  the  species  was  first  described  as  Hypoclinea 
Jiumilis  by  Dr.  G.  Mayr,  in  1868,  from  workers  collected  in  1866  near 
Buenos  Aires  in  Argentina,  the  original  description  appearing  in  the 
Annuario  della  Societa  dei  Naturalisti  di  Modena,  volume  3,  page 
164.  Following  is  Mayr's  description  of  the  species  kindly  fur- 
nished by  Dr.  W.  M.  Wheeler,  of  the  Bussey  Institution,  Harvard 
University,  from  the  original  edition: 

Operia:  Long.  2.6  mm.  Sordide  ferruginea,  micans,  mandibularum  parte  apicali 
flavescenti,  abdomine  nigrofusco,  tarsis  et  nonnunquam  tibiis  testaceis;  microscopice 
adpresse  pubescens;  absque  pilis  abstantibus;  subtilissime  coriaceo-rugulosa,  mandi- 
bulis  nitidis  sublaevigatis  punctis  nonnullis;  clypeus  margine  antico  late  haud  pro- 
funde  emarginatus;  thorax  inter  mesonotom  et  metanotum  paulo  et  distincte  eon- 
strictus,  pronoto  fornicato,  mesonoto  longitrorsum  recto,  transversim  convexo,  meta- 
noto  inermi  longitrorsum  fornicato,  pronoto  paulo  altiori;  petioli  squama  compressa 
rotundata. 

At  the  request  of  the  senior  author,  Dr.  Wheeler  prepared  the  fol- 
lowing redescription  of  the  worker,  and  descriptions  of  the  queen 
and  male,  thus  making  a  complete  and  comprehensive  description 
of  the  species: 

Iridomyrmex  humilis  Mayr. 

Worker:  Length  2.2-2.6  mm. 

Head  oval,  broader  behind  than  in  front,  with  its  posterior  margin  slightly  concave 
in  the  middle.  Eyes  flattened,  in  front  of  the  middle  of  the  head.  Mandibles  with 
two  larger  apical  and  several  minute  basal  teeth.  Clypeus  short,  convex  in  the  mid- 
dle, with  broadly  excised  anterior  margin.  Frontal  area  and  groove  present  but 
rather  indistinct.  Antennal  scapes  extending  about  one-fourth  their  length  beyond 
the  posterior  corners  of  the  head.  Joints  1-5  and  the  terminal  joint  of  the  funiculus 
distinctly  longer  than  broad;  remaining  joints  nearly  as  broad  as  long.  Thorax  slen- 
der, narrower  than  the  head;  broadest  through  the  pronotum  which  is  convex,  rounded 
and  nearly  as  long  as  broad.  Mesonotum  nearly  as  long  as  the  pronotum,  sloping, 
laterally  compressed,  in  profile  evenly  continuing  the  contour  of  the  pronotum.     Me- 

1  An  undetermined  species  of  Iridomyrmex,  apparently  introduced,  has  been  found  by  Dr.  W.  M.  Wheeler 
In  a  greenhouse  at  Boston,  Mass. 


28 


THE  ARGENTINE  ANT. 


Boepinotal  constriction  rather  deep,  extending  obliquely  downward  and  backward  oil 
each  side.  Epinotum  short,  nearly  twice  as  high  as  long,  convex  on  the  sides,  with 
a  short  convex  base,  and  a  longer,  flatter  and  more  sloping  declivity.  Petiole  small, 
less  than  half  as  broad  as  the  epinotum;  its  scale  in  profile,  compressed,  cuneate, 
inclined  forward,  with  flattened  anterior  and  posterior  surfaces  and  rather  acute  apex; 
seen  from  behind  its  border  is  entire  and  evenly  rounded  or  even  slightly  produced 
upward  in  the  middle.     Gaster  small.     Legs  rather  slender. 


Fio.  G.— The  Argentine  ant,  adult  forms:  a,  Adult  male;  al,  head  of  male;  a2,  petiole  of  male;  b,  worker; 
bl,  head  of  worker;  b2,  petiole  of  worker;  c,  fertile  queen;  cl,  head  of  queen:  c2,  petiole  of  queen.  All 
greatly  enlarged.    (Senior  author's  illustration.) 


Body  minutely  shagreened  or  coriaceous,  subopaque  and  glossy;  mandibles,  clypeus 
and  anterior  border  of  the  head  more  shining.  Mandibles  minutely  and  rather  ob- 
scurely punctate. 

Hairs  few,  suberect,  yellowish,  confined  to  the  mandibles,  clypeus,  tip  and  lower 
surface  of  the  gaster.  Pubescence  short  and  uniform,  grayish,  so  that  the  body  has  a 
slightly  pruinose  appearance. 


SYSTEMATIC    POSITION.  29 

Brown;  thorax,  scapes  and  legs  somewhat  paler;  mandibles  yellowish;  apices  of 
the  individual  funicular  joints  blackish. 

Female  (dealated):  Length  4.5-5  mm. 

Head,  without  the  mandibles,  but  little  longer  than  broad,  with  rather  angular  pos- 
terior corners,  straight,  subparallel  sides  and  straight  posterior  border.  Eyes  large  and 
rather  convex.  Mandibles  and  clypeus  like  that  of  the  worker,  scapes  proportionally 
shorter  and  stouter.  Thorax  large,  as  broad  as  the  head,  elongate  elliptical,  nearly 
three  times  as  long  as  broad.  In  profile  the  scutellum  is  very  convex,  projecting 
above  the  meso-  and  epinotum.  Epinotum  with  very  short  base  and  long  abrupt 
declivity.  Petiolar  node  erect,  more  than  half  as  broad  as  the  epinotum.  Gaster 
elliptical,  somewhat  shorter  and  a  little  broader  than  the  thorax.     Legs  slender. 

Sculpture  like  that  of  the  worker  but  more  opaque;  mandibles  and  clypeus  also 
less  shining. 

Scattered  hairs  more  numerous  than  in  the  worker  and  also  present  in  small  numbers 
on  the  vertex,  gula,  mesonotum,  presternum,  and  fore  coxae.  There  is  also  a  row  of 
short  hairs  along  the  posterior  margin  of  each  gastric  segment.  Pubescence  dis- 
tinctly longer,  more  silky,  and  denser  than  in  the  worker. 

Dark  brown;  antennae,  legs  and  posterior  margins  of  the  gastric  segments  reddish; 
mandibles,  sutures  of  thorax  and  articulations  of  legs  yellow. 

Male:  Length  2.8-3  mm. 

Head  much  flattened;  including  the  flattened  eyes,  as  broad  as  long.  Vertex  and 
ocelli  prominent.  Cheeks  short.  Mandibles  small,  overlapping,  with  a  single,  acu- 
minate apical  tooth.  Anterior  clypeal  border  straight.  Antennae  slender;  scape 
only  between  three  and  four  times  as  long  as  broad;  first  funicular  joint  globose, 
broader  than  any  of  the  other  joints;  second  joint  much  longer  than  the  -cape;  joints 
3-5  growing  successively  shorter;  joints  6-12  considerably  shorter  and  more  slender. 
Thorax  very  robust,  elliptical,  broader  than  the  head,  which  is  over-arched  by  the 
protruding,  rounded  mesonotum.  Scutellum  even  more  prominent  than  in  the  female. 
Epinotum  with  subequal  base  and  declivity,  the  former  slightly  convex,  the  latter 
feebly  concave,  forming  an  angle  with  each  other.  Petiole  small,  its  node  with  rather 
blunt  margin,  slightly  inclined  forward.  Gaster  very  small,  elongate  elliptical,  with 
small  rounded  external  genital  valves.  Legs  slender.  Wings  with  a  four-sided  discal 
cell  and  two  well  developed  cubital  cells.  The  costal  margin  is  depressed  or  folded 
in  just  proximally  to  the  stigma. 

Sculpture,  pilosity  and  pubescence  as  in  the  worker;  color  more  like  that  of  the 
female,  except  that  the  antennae,  legs,  mandibles  and  internal  genitalia  are  pale, 
sordid  yellow.     Wings  smoky  hyaline,  with  brown  veins  and  stigma. 

i".  humilis  belongs  to  a  small  group  of  neotropical  species  embracing  also  I.  iniquus 
Mayr,  dispertitus  Forel,  heiteli  Forel  and  melleus  Wheeler.  The  workers  of  Iceiteli  and 
melleus  may  be  at  once  distinguished  by  their  color,  the  former  having  a  yellowish 
brown  head  and  thorax  and  the  remaining  parts  brownish  yellow;  the  latter  being 
pale  yellow  with  a  blackish  gaster  and  funiculus.  In  these  and  in  I.  iniquus  and 
dispertitus  the  mesoepinotal  constriction  is  much  deeper  than  in  humilis  and  the  meso- 
and  epinotum  are  of  a  different  shape.  The  mesonotum  in  profile  does  not  form  a 
continuous,  even  line  with  the  pronotum  and  the  epinotum  is  very  protuberant  and 
almost  conical,  i".  humilis  represents  a  transition  from  the  above  group  of  species 
to  that  of  I.  analis  Em.  Andre,  which  is  very  common  in  the  Southern  States.  This 
species  has  a  shorter,  more  robust  thorax,  more  like  that  of  Tapinoma,  and  much  less 
constricted  in  the  mesoepinotal  region. 

The  above  description  was  drawn  from  a  number  of  workers,  males  and  females 
taken  from  the  same  nest  in  Baton  Rouge,  La.,  by  Mr.  Wilmon  Newell.  The  types 
described  by  Mayr  were  captured  by  Prof.  P.  de  Strobel  in  the  environs  of  Buenos 
/ires. 


30  THE   ARGENTINE  ANT. 

RESEMBLANCE   TO    OTHER   ANTS. 

There  is  little  difficulty  in  distinguishing  Iridomyrmex  Jiumilis 
Mayr  from  its  nearest  American  relative,  Iridomyrmex  analis  Ern. 
Andre.  The  latter  species  is  quite  common  in  cotton  fields  and  other 
situations  in  the  South,  is  much  lighter  in  color  than  Jiumilis,  and 
possesses  a  very  disagreeable  odor  which  is  entirely  lacking  in  the 
case  of  Jiumilis.  The  clearly  marked  trails  of  the  Argentine  workers, 
when  on  their  foraging  expeditions  or  when  moving  from  place  to 
place,  have  no  counterpart  in  the  case  of  analis,  the  workers  of  which 
in  large  measure  forage  independently  of  each  other.  /.  analis 
constructs  inverted  cone-shaped  mounds  or  craters  on  the  surface 
above  the  underground  nests,  while  what  little  dirt  is  excavated  by 
Jiumilis  is  scattered  about  the  entrance  to  the  nest  in  promiscuous 
fashion,  the  ants  evidently  desiring  to  rid  themselves  of  the  exca- 
vated pellets  as  expeditiously  and  conveniently  as  possible.  The 
"  wet-weather  sheds "  of  the  Argentine  ant,  constructed  only  during 
or  just  after  prolonged  rainy  spells,  bear  no  resemblance  whatever 
to  the  craters  of  analis;  but  on  the  contrary  are  more  or  less  flat, 
composed  of  fine  particles  of  earth,  unstable  in  structure  and  supported 
by  grass  or  leaves. 

However,  the  superficial  resemblance  of  /.  Jiumilis  to  several  spe- 
cies of  other  genera  is  even  closer  than  to  I.  analis  and  is  sufficient 
to  make  positive  identification  of  Jiumilis  well-nigh  impossible  ex- 
cept by  one  skilled  in  detecting  the  characters  used  by  myrmecolo- 
gists  for  classification.  Among  the  southern  forms  most  likely  to 
be  mistaken  for  /.  Jiumilis,  and  vice  versa,  may  be  mentioned  the 
"crazy  ant"  (Prenolepis  longicornis  Fab.)  and  Dorymyrmex  pyra- 
micus  Roger.  The  workers  of  both  these  species  are  of  practically 
the  same  size  and  color  as  those  of  Jiumilis  and  the  workers  of  all  three 
travel  and  forage  in  much  the  same  way.  Prenolepis  is  distinguished 
from  I.  Jiumilis  by  its  camponotine  characters,  particularly  the  shape 
of  the  gizzard,  by  the  cloacal  orifice  being  round  rather  than  slit- 
shaped,  and  by  the  presence  of  stiff,  erect  hairs  upon  the  body.  Dory- 
myrmex is  easily  distinguished  by  the  conical  or  pointed  elevation 
upon  the  epinotum  (last  dorsal  segment  of  the  thorax),  a  structure 
that  is  entirely  lacking  in  Iridomyrmex,  the  epinotum  of  which  is 
evenly  convex. 

The  resemblance  of  /.  Jiumilis  to  still  other  species  is  sufficient  to 
be  confusing  at  times,  but  one  can,  by  a  process  of  eliminating  certain 
easily  observed  characteristics,  determine  with  reasonable  probability 
whether  a  colony  of  living  ants  belongs  to  this  species  or  not.  First 
to  be  noticed  is  the  size  of  the  ants  under  suspicion.  The  workers  of 
the  Argentine  ant  are  from  2.2  to  2.6  mm.  in  length,  the  largest  indi- 


SYSTEMATIC   POSITION.  31 

vidual  we  have  ever  seen  measuring  2.75  mm.  If  workers  are  more 
than  3  mm.  or  less  than  2  mm.  in  length,  it  may  be  safely  concluded 
that  the  ant  under  observation  is  of  some  other  species.  The  Argen- 
tine queen,  however,  is  from  4.5  to  5  mm.  in  length.  The  color  of 
the  Argentine  ants — all  adult  forms — is  a  very  deep  brown,  almost 
approaching  black,  and  the  color  is  uniform  over  the  entire  body. 
The  possession  of  head  and  thorax  of  one  color  with  abdomen  of  a 
different  color  immediately  eliminates  a  specimen  from  this  species. 
A  colony  containing  workers  of  more  than  one  size  is  also  ehminated, 
since  all  Argentine  workers  are  of  one  size  or  caste.  The  fact  that  the 
petiole  or  pedicel  (connecting  joint  between  the  thorax  and  abdomen) 
of  /.  liumilis  consists  of  only  one  segment  readily  distinguishes  it  from 
the  species  of  Solenopsis  and  other  myrmicine  ants.  The  pupae  of 
our  species  is  never  inclosed  in  cocoons,  but  always  naked,  with  legs, 
eyes,  segments,  etc.,  plainly  visible.  Argentine  workers,  when 
crushed  between  the  fingers,  give  no  perceptible  odor,  and  this  readily 
distinguishes  them  from  their  closest  relative,  /.  analis,  as  well  as 
from  their  more  remote  relatives,  the  species  of  Tapinoma.  The 
Argentine  worker  does  not  possess  a  functional  sting  and  does  not 
even  attempt  to  sting.  This  again  separates  the  workers  from  those 
of  a  great  many  species,  including  Solenopsis,  most  of  which  sting 
viciously  upon  the  slightest  provocation.  Upon  being  disturbed, 
particularly  in  the  nest,  some  of  the  Argentine  workers  will  attempt 
to  bite,  but  by  far  the  great  majority  devote  their  energies  to  escaping 
rapidly  or  to  removing  the  larvae  and  pupae  to  a  place  of  safety. 
What  few  do  attempt  to  bite  are  not  successful  in  piercing  the  skin 
of  one's  hands  owing  to  their  weak  jaws.  It  is  only  when  reaching 
tender  places,  such  as  the  skin  between  the  bases  of  the  fingers  for 
example,  that  they  are  able  to  make  their  bites  effective. 

If,  therefore,  ants  suspected  of  being  Iridomyrmex  liumilis  meet  the 
following  qualifications,  and  in  addition  exhibit  the  habits  already 
described,  there  is  a  reasonable  probability  that  they  belong  to  this 
species,  and  examples  should  be  submitted  to  a  specialist  for  exam- 
ination : 

Workers  not  over  3  mm.  nor  less  than  2  mm.  in  length 

Workers  uniformly  colored;  deep  brown,  nearly  black. 

Workers  of  uniform  size;  no  distinction  as  to  caste. 

Workers  traveling  in  well-defined  trails  or  lines  to  and  from  the  nest. 

Workers  emitting  no  offensive  odor  when  crushed. 

Workers  unable  to  sting  and  unable  to  bite  effectively. 

Pup^p  not  inclosed  in  cocoons. 

Petiole  or  pedicel  consisting  of  only  one  segment. 

Petiole  prolonged  dorsally  into  a  wedge-shaped  scale,  inclined  slightly  forward. 

Epinotum  devoid  of  a  pointed  or  conical  elevation. 

Ocelli  absent  in  workers,  present  in  queens  and  males. 


32  THE   ARGENTINE  ANT. 

METHODS  OF  STUDY. 

When  the  study  of  this  ant  was  undertaken,  two  requisites  presented 
themselves — a  type  of  artificial  formicary  in  which  continuous  obser- 
vations could  be  made  and  individuals  kept  track  of  from  the  time  of 
egg  deposition  until  the  adult  stage  was  reached,  and  some  method 
by  which  all  individuals  of  a  colony  could  be  confined  to  their  own 
formicary. 

Space  need  not  be  taken  to  describe  the  types  of  artificial  formicaries 
which  were  not  successful. 

The  Janet  cages  proved  successful  only  in  the  case  of  very  large 
colonies,  but  in  these  the  multiplicity  of  individuals  made  accurate 
observations  impossible.  It  may  be  remarked  that  this  type  of  cage 
is  excellent  for  studying  the  community  life  as  a  whole  and  for  making 
experiments  with  poisons  or  with  parasitic  fungi  or  bacteria. 

Cages  totally  inclosed  were  not  successful,  for  the  reason  that  the 
ants,  when  deprived  of  the  privilege  of  leaving  their  nest,  failed  to  act 
in  a  normal  manner. 

The  cage  finally  adopted  was,  with  modifications,  the  one  described 
by  Sir  John  Lubbock  on  pages  2  and  3  of  his  classic  work.1  This 
consists  essentially  of  two  glass  plates  containing  between  them  a 
layer  of  pulverized  earth  in  which  the  ants  may  burrow  at  their 
pleasure.  Considerable  difficulty  was  experienced  in  getting  the 
glass  plates  the  proper  distance  apart;  if  too  far  apart  the  ants  could 
make  burrows  wilich  were  not  open  to  observation,  and  if  too  close 
together  insufficient  room  was  afforded  the  queen  in  which  to  stand 
and  Walk  upright.  As  the  queen  is  about  twice  as  tall  as  the  worker, 
it  seemed  for  a  time  that  a  suitable  cage  could  not  be  constructed. 
After  repeated  trials,  however,  it  was  found  that  if  the  space  between 
the  glass  plates  wrere  made  exactly  1.75  mm.  the  queen  would  have 
sufficient  room  and  the  workers  could  not  construct  invisible  galleries. 

This  type  of  cage  and  its  supporting  stand  are  well  illustrated  by 
figures  7  and  8.  Figure  7  shows  the  several  parts  of  the  cage;  3  is  the 
cage  proper,  consisting  of  two  plates  of  glass  held  uniformly  1.75 
millimeters  apart  by  strips  of  leather  at  all  four  edges,  a  door  or  open- 
ing being  left  at  one  corner.  (See  fig.  9.)  Old  negatives,  the  films 
removed  with  caustic  soda,  have  been  found  the  most  desirable  for 
making  these  cages,  both  because  such  glass  is  remarkably  clear  and 
free  from  imperfections  and  because  it  is  of  uniform  thickness.  The 
size  of  the  cage  may  vary  from  3|  by  4J  up  to  8  by  10  inches  or  even 
larger.  Leather  w7as  found  more  satisfactory  for  making  the  edges 
of  the  cage  than  either  glass  or  wood.  The  strip  of  leather  between 
the  glass  margins  is  about  -J-  inch  in  width.  It  is  extremely  difficult 
to  find  a  strip  of  glass  uniformly  1.75  millimeters  thick  and  it  is  also 

•  Avebury.    Ants,  bees,  and  wasps,  1881. 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  II. 


A  Small  Colony  of  Argentine  Ants  as  Seen  in  one  of  the  Artificial  Formicaries. 

(Original.) 


METHODS    OF    STUDY. 


33 


difficult  to  attach  one  piece  of  glass  to  another  firmly.  Wooden 
strips  present  the  disadvantage  of  quickly  decaying  and  of  warping, 
no  matter  what  glue  or  cement  is  used  to  hold  them  in  position.  Since 
it  is  sometimes  desirable  to  place  moist  earth  in  the  cages,  or  to  add 
moisture  from  time  to  time,  a  waterproof  cement  is  most  desirable 
for  attaching  the  glass  plates  to  the  leather  strip.  The  space  between 
the  glass  plates  is  filled  with  finely  pulverized  earth  after  completion 
and  drying  of  the  cage,  and  in  this  the  ants  are  permitted  to  burrow 
and  construct  galleries  as  they  please.     (See  PL  II.) 

The  cage  proper  is  supported  on  a  platform  (1 )  which  in  turn  rests 
firmly  upon  a  standard  (2)  having  a  base  (4).  The  platform  must 
have  its  upper  surface  perfectly  level  and  it  must  remain  so  for  an 


Fig.  7.— Artificial  formicary  or  cage  used  in  studying  the  Argentine  ant:  1,  Supporting  platform;  2,  stand- 
ard; 3,  cage  proper,  made  of  glass  and  leather,  containing  earth;  4,  hase;  5,  cover.  (Senior  author's 
illustration.) 

indefinite  time,  otherwise  the  ants  will  take  up  their  abode  between 
the  cage  and  platform  rather  than  in  the  cage  itself.  The  platform  is 
therefore  made  of  two  pieces  of  even,  seasoned  cypress  J-  inch  thick, 
screwed  together  with  numerous  screws  and  with  the  grain  of  the 
two  pieces  at  right  angles  to  each  other.  On  this  platform  the  cage 
rests  without  fastenings  of  any  kind.  The  cover  (-5)  is  constructed  of 
two  pieces  of  cypress  in  the  same  manner  as  the  platform,  but  in 
addition  has  an  iron  handle  attached  to  its  upper  surface  and  has  a 
piece  of  felt  glued  to  its  under  surface,  so  that,  when  it  is  placed  upon 
the  cage  proper,  all  light  is  excluded  except  at  the  entrance.  The 
cover  is  of  the  same  outside  dimensions  as  the  cage  itself.  To  insure 
the  platform  remaining  level  it  is  often  necessary  to  make  the  base 
75508°— Bull.  122—13 3 


34 


THE   ARGENTINE   ANT. 


of  two  pieces  in  the  same  manner  as  the  platform,  or  to  nail  strips 
across  it  at  right  angles  to  the  grain.  Both  platform  and  base  are 
attached  to  the  standard  by  long  screws  with  heads  countersunk. 
Food  is  furnished  by  placing  it  on  a  piece  of  cardboard  at  any  point 
on  the  cover  or  platform.  The  base  stands  in  running  water,  as 
explained  below.  This  type  of  cage  permits  the  ants  to  leave  their 
nest  within  the  cage  and  to  forage  over  the  platform,  cover,  and  stand 
in  natural  fashion,  but  their  escape  from  the  stand  is  prevented  by  the 
very  natural  barrier  of  water,  which  they  find  when  they  approach  the 
bottom  of  the  standard.  It  is  not  possible  for  them  to  conceal  larva?, 
or  eggs  where  the  observer  can  not  find  them  and  they  can  not  bring 


Fig.  8.— Artificial  formicary  with  parts  assembled  ready  for  use.    (Senior  author's  illustration.) 

in  larva?  or  pupa?  from  outside  sources  to  the  annoyance  and  vexation 
of  the  student. 

While  the  ants  are  very  fond  of  sweets,  we  have  found  that  sweets 
alone  will  not  suffice  for  food  indefinitely.  Animal  food  is  also 
required,  and  we  find  that  by  supplying  the  colonies  with  a  ''balanced 
ration"  of  honey  and  fresh  beef  or  veal  they  will  work  in  a  perfectly 
natural  manner  for  many  months  without  other  food. 

The  problem  of  confining  the  ants  to  the  cage  and  its  stand  was  not 
so  easily  solved.  We  first  tried  Sir  John  Lubbock's  method  of  plac- 
ing a  moat  of  glycerine  or  water  about  the  stand,  but  both  liquids 


METHODS   OF    STUDY. 


35 


dried  too  quickly  and  were  effective  for  only  a  few  hours.  Recourse 
was  had  to  the  proverbial  chalk  line  without  success.  Bands  or 
ditches  of  kerosene,  crude  oil,  tar,  oils  of  sassafras  and  citronella,  tree 
tanglefoot,  zenoleum,  naphthaline,  coal-tar  disinfectants,  whale-oil 
soap,  sharp-edged  tin,  and  fur  were  all  failures.  Certain  powerful 
odors,  such  as  those  of  zenoleum,  sassafras,  and  citronella,  act  as 
repellents  temporarily,  but  after  a  few  hours  of  evaporation  are  no 
longer  effective.  Ordinarily  these  ants  will  not  cross  bands  of  cotton 
tape  which  have  been  impregnated  with  a  saturated  solution  of  cor- 
rosive sublimate  and  dried,  but  when  attempting  to  leave  an  area  to 
which  they  have  been  confined  by  this  means  they  are  much  more 
persistent  in  crossing  it. 

Water  with  a  film  of  whale-oil  soap  on  it  acted  as  a  repellent  for  a 
few  hours  only,  while  a  film  of  kerosene  upon  water  merely  afforded 


Fig.  9. — Entrance  of  artificial  formicary  shown  in  figures  7  and  8.    (Senior  author's  illustration.) 

a  convenient  floor  upon  which  the  ants  could  travel.  The  difficulty 
in  confining  the  workers  with  any  liquid  or  mucilaginous  substance 
lies  in  the  fact  that  they  are  exceedingly  light,1  and  sticky  substances 
shortly  harden  on  the  surface,  so  that  the  workers  are  supported. 
The  surface  film  of  clear  water  is  in  fact  almost  strong  enough  to  sup- 
port a  "worker  not  loaded.  It  is  not  unusual  to  see  an  ant  alternately 
walking  and  swimming  in  crossing  a  narrow  ditch  of  water  which  has 
been  standing  for  a  few  hours.  Minute  dust  particles  collecting  upon 
standing  water  shortly  form  a  film  upon  which  the  workers  pass  with 
ease.  Perfectly  fresh  water  therefore  served  to  confine  the  colonies 
to  their  cages,  and  at  first  our  observations  were  made  upon  colonies 
in  cages  which  were  standing  in  dishes  of  water.  This,  however, 
necessitated  frequent  changing  of  the  water,  and  observations  were 
often  brought  to  an  abrupt  finish  by  other  duties  which  prevented 
the  change  of  water  in  the  vessels  at  the  right  time. 

1  The  average  weight  of  one  worker  is  0.0002077  gram. 


36  THE   ARGENTINE   ANT. 

In  February,  1908,  the  senior  author  constructed,  on  the  grounds 
of  the  Louisiana  Experiment  Station  at  Baton  Rouge,  a  small  build- 
ing for  the  purpose  of  studying  this  ant  more  in  detail.  The  building 
was  10  by  30  feet  and  equipped  with  benches  having  upon  them  gal- 
vanized iron  trays  2\  by  12  feet,  4  inches  deep.  In  these  trays  the 
cages  were  placed  and  by  means  of  suitable  connections  running 
water  2  inches  in  depth  was  kept  passing  through  the  trays  day  and 
night.  As  the  ants  would  not  voluntarily  enter  running  water  this 
arrangement  worked  admirably.  The  interior  arrangement  of  this 
building  is  shown  in  Plate  III.  The  iron  trays  and  ant  cages  are 
shown  upon  the  right,  with  work  tables,  chemicals,  etc.,  on  the  left. 
The  building  was  equipped  with  electric  and  extension  lights  for 
night  examinations,  and  a  combined  thermograph  and  hygrograph 
recorded  the  temperature  and  humidity  of  the  room  at  all  times. 
For  convenience  this  building  was  referred  to  as  the  "formicarium.,, 
Plenty  of  windows  insured  full  ventilation  at  all  seasons,  and  to  avoid 
abnormally  high  temperature  in  summer  a  second  or  accessory  roof 
was  placed  two  feet  above  the  main  roof.  This  laboratory  also 
proved  a  convenient  insectary  for  the  rearing  of  other  insects. 

The  Argentine  ant  possesses  a  marked  proclivity  for  attacking  all 
insects  which  one  has  under  observation,  and  all  rearing  experiments  in 
cages,  no  matter  what  the  insect,  must  be  protected  from  the  ants. 
The  trays  of  running  water  therefore  served  to  keep  the  ants  away 
from  general  cage  experiments  as  well  as  to  confine  them  to  the  cages 
in  which  they  themselves  were  being  studied. 

ESTABLISHING    COLONIES    FOR    STUDY. 

To  establish  a  colony  in  one  of  the  artificial  formicaries  or  cages  is 
comparatively  easy.  It  is  only  necessary  to  secure  a  fertile  queen 
from  some  thriving  outdoor  colony  and  place  her  on  the  stand,  first 
placed  in  water,  together  with  any  desired  number  of  workers  which 
have  been  captured  by  attracting  them  to  a  sweetened  sponge  or 
piece  of  fresh  meat.  Any  lot  of  workers  will  accept  any  queen  and 
vice  versa.  When  queen  and  workers  are  thus  placed  upon  the  cage 
and  its  stand,  they  usually,  after  a  few  hours,  take  up  their  abode 
in  the  nest  proper.  At  first  we  experienced  some  difficulty  in  pre- 
venting them  from  collecting  beneath  the  stand,  but  it  was  presently 
found  that  if  a  little  dirt  were  removed  from  another  colony  and  placed 
in  the  entrance  of  the  new  formicary  the  ants  would  enter  at  once  and 
adopt  it  as  a  suitable  home.  After  the  establishment  of  such  colonies 
the  queen  usually  commences  egg  deposition  in  from  6  to  48  hours. 

By  establishing  colonies  in  this  manner,  without  immature  stages 
present,  it  is  easy  to  observe  the  daily  rate  of  egg  deposition,  the 
incubation  period  of  the  eggs,  and  the  duration  of  the  larval  and  pupal 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  III. 


METHODS   OF   STUDY.  37 

stages.  In  some  of  the  records  given  below  single  individuals  have 
been  kept  under  observation  from  deposition  of  the  egg,  through  larval 
and  pupal  stages,  to  the  adult.  In  other  cases  the  time  from  deposi- 
tion of  the  first  egg  until  hatching  of  the  first  larva  was  assumed  to  be 
the  period  of  incubation,  date  of  hatching  of  first  larva  to  formation 
of  first  pupa  the  duration  of  the  larval  period,  etc. 

While  these  cages  were  invaluable  in  studying  the  life  history  of  the 
ants,  the  small  amount  of  space  available  for  them  between  the  glass 
plates  made  the  number  of  ants  they  would  contain  very  limited.  For 
the  purpose  of  studying  the  general  habits  of  large  colonies  of  ants  a 
modification  of  the  J  anet  cage  was  used.  As  its  name  implies,  this  cage 
was  invented  by  Mr.  Charles  Janet,1  and  is  described  by  him  as  follows: 

The  apparatus  (an  artificial  horizontal  nest  of  porous  mineral  substance)  described 
in  this  treatise  gives,  in  reference  to  the  raising  of  ants,  remarkable  results.  Ants  die 
in  a  short  time  when  placed  where  they  can  not  receive  sufficient  moisture ;  but  (and 
this  is  the  delicate  point)  this  moisture  must  be  maintained  within  certain  limits. 
The  apparatus  invented  up  to  the  present  do  not  solve  this  difficulty.  Furthermore, 
they  do  not  lend  themselves  easily  to  observation,  nor  do  they  permit  one  to  withdraw 
with  ease  specimens  when  needed.  The  artificial  nest  is  formed  of  a  block  of  plaster, 
or  any  other  porous  substance,  which  has  hollowed  out  of  it  a  certain  number  of  small 
cells,  placed  one  after  the  other  and  communicating.  These  cells  are  covered  with  an 
opaque  slab  designed  to  keep  the  cells  dark  between  the  periods  of  observation.  A  cup 
of  water  placed  at  the  end  of  the  block  allows  it  to  absorb  moisture.  The  cell  nearest 
this  cup  is  the  dampest,  and  the  one  farthest  away  the  driest.  I  leave  this  last  always 
light  so  that  it  resembles,  for  the  breeding  under  observation,  a  space  outside  of  the 
nest.  If  the  water-cell  has  been  kept  too  moist,  the  ants  go  into  the  cell  farthest  away, 
that  is  to  say  the  driest.  When,  on  the  contrary,  the  apparatus  becomes  too  dry  the 
ants  return  to  the  walls  of  the  cell  containing  the  water,  which  is  always  damper  than 
the  other  parts  of  the  nest.  They  can  thus  choose  for  themselves  the  part  of  the  nest 
presenting  the  degree  of  moisture  which  suits  them  best. 

The  chief  modification  adopted  was  the  use  of  a  five-celled  cage 
instead  of  one  of  four  cells,  as  described  by  Janet.  Also,  the  ants 
were  not  inclosed  within  the  cage,  but  were  allowed  to  enter  or  leave 
at  will.  To  permit  of  this  the  Janet  cages  were  placed  upon  plat- 
forms, which  stood  in  running  water.  These  platforms  were  consid- 
erably larger  than  the  cages,  and  this  gave  the  workers  quite  an  area 
to  forage  over,  simulating  natural  conditions  quite  closely.  The  food 
was  placed  upon  the  platform,  outside  the  nest,  and  the  workers  thus 
had  to  carry  it  in  and  feed  the  larvae  in  the  same  manner  in  which  it 
was  done  outdoors.  These  cages  had  sufficient  capacity  for  many 
thousands  of  ants.  They  were  used  for  observing  the  behavior  of 
large  colonies  and  for  the  purpose  of  noting  the  effects  of  poisons 
and  various  control  measures. 

1  Studies  on  ants.  Note  2.  Apparatus  for  the  raising  and  observation  of  ants  and  other  small  animals 
which  require  a  moist  atmosphere.  Extract  Ann.  Ent.  Soc.  France,  Mar.  10,  1893;  vol.  62,  pp.  467-482, 
figs.  11-12.     (Translated  by  Miss  A.  O 'Conor.) 


38  THE    ARGENTINE    A  XT. 

LIFE  HISTORY, 
THE   EGG. 
(PI.  IV,  A.) 

The  egg  is  elliptical,  pearly  white,  lustrous,  without  markings,  and 
the  membrane  is  extremely  thin  and  delicate.  The  surface  is  some- 
what mucilaginous,  so  that  when  eggs  come  in  contact  they  adhere 
to  each  other.  This  enables  the  workers  to  handle  them  en  masse  and 
also  permits  of  their  being  deposited  upon  the  walls  or  ceilings  of  the 
ants'  habitations. 

The  average  size  is  0.3  mm.  long  by  0.2  mm.  wide.  The  largest  egg 
encountered  while  measuring  a  series  was  0.34  mm.  long  by  0.24  mm. 
wide,  and  the  smallest  0.27  mm.  by  0.1S7  mm. 

As  time  for  hatching  approaches  the  luster  fades  and  the  surface 
takes  on  a  dull  appearance.  This  is  not  sufficiently  pronounced  and 
uniform,  however,  to  be  taken  as  a  safe  guide  to  immediate  hatching. 
When  the  embryo  takes  on  the  larval  shape  the  membrane  not  infre- 
quently adapts  itself  in  a  way  to  the  general  contour  of  the  inclosed 
embryo,  thus  making  it  very  difficult  to  distinguish  between  the  eggs 
and  the  newly-hatched  larvae. 

In  the  large  Janet  style  cages  the  workers  seem  to  take  elaborate  care 
of  the  eggs  in  order  to  secure  for  them  just  the  requisite  amount  of 
humidity.  Frequently  they  will  be  shifted  several  times  in  the  course 
of  the  day,  first  being  stored  in  one  corner,  then  moved  to  the  center 
of  the  compartment,  afterwards  carried  to  another  compartment,  and 
perhaps  finally  stuck  to  the  glass  ceiling.  Sometimes  the  eggs  are 
separated  from  the  larvae  and  pupae;  at  other  times  they  will  be  stored 
together  in  apparently  hopeless  confusion. 

The  care  of  the  eggs  by  tne  workers  seems  essential  to  complete 
embryonic  development.  Eggs  deposited  in  test  tubes  by  isolated 
queens  have  gone  through  a  portion  of  the  embryonic  development, 
but  we  have  not  been  successful  in  getting  them  to  hatch.  This  may 
be  due  in  part  to  the  ease  with  which  the  delicate  embryos  are  injured 
in  handling  and  to  the  fact  that  when  placed  on  glass  the  condensing 
moisture  may  retard  or  stop  development. 

The  queen  appears  to  act  merely  as  an  egg-producing  machine,  and 
once  the  egg  has  been  deposited  she  pays  no  further  attention  to  it. 
The  act  of  oviposition  has  been  observed  several  times  and  does  not 
occupy  more  than  a  few  seconds  of  time.  An  attendant  ant  appears 
to  be  anxiously  watching  for  the  appearance  of  the  egg,  and  it  is 
immediately  picked  up  and  rushed  off  to  the  nearest  "egg  pile/' 
sometimes  before  it  has  time  to  touch  the  floor  of  the  nest. 

Attempts  to  get  fertilized  queens,  unattended  by  workers,  to 
deposit  eggs  and  rear  the  resulting  larvae  to  maturity  have  been 
unsuccessful.  Such  queens  stop  laying  a  few  days  after  their  isola- 
tion and  seemingly  pay  no  attention  to  what  few  eggs  they  do  deposit. 


LIFE    HISTORY 


39 


Eggs  are  deposited  at  all  seasons  of  the  year.  The  large  majority 
of  them  are  produced  during  the  summer,  but  a  few  are  laid  in  warm 
spells  during  the  winter  months.  The  rate  of  deposition  has  not  been 
determined,  but  one  queen  under  observation  in  a  cage  deposited 
at  the  rate  of  30  eggs  per  day,  now  and  then  suspending  oviposition 
for  several  days  at  a  time. 

In  outdoor  colonies  oviposition  ceases  when  the  daily  mean  tem- 
perature drops  below  65°  F.,  but  is  usually  begun  again  when  the 
mean  temperature  rises  above  this  point,  regardless  of  the  time  of  the 
year. 

No  indication  has  been  found  of  workers  depositing  eggs,  even  in 
colonies  that  were  queenless  for  long  periods;  neither  did  queenless 
colonies  ever  rear  queens  from  the  eggs  and  larvae  present  in  the  nest 
at  the  time  queenlessness  occurred. 


PERIOD    OF    INCUBATIOX. 


The  period  of  incubation  varies  with  the  season  of  the  year,  and 
in  proportion  as  the  temperature  remains  high  or  low.  The  shortest 
incubation  period  observed  has  been  12  days,  the  longest  55  days, 
and  the  average  is  about  28  days.  The  longer  periods  are  doubtless 
accounted  for  by  the  entire  suspension  of  embryonic  development 
during  cool  weather,  and  it  is  not  impossible  that  the  viability  of 
eggs  may  be  entirely  destroyed  by  a  temperature  as  low  as  25°  or 
30°  F.,  but  on  this  point  more  data  are  needed. 

The  period  of  incubation  has  been  determined,  ordinarily,  by 
placing  a  queen  and  workers,  but  no  immature  stages,  in  an  artificial 
formicary  and  then  noting  the  time  from  deposition  of  the  first  egg 
to  appearance  of  the  first  larva.  Tin's  period  was  assumed  to  be  the 
real  period  required  for  incubation.  In  other  cases  single  groups  of 
eggs  have  been  kept  under  constant  observation  throughout  the 
entire  period  of  incubation.  The  following  table  shows  the  variation 
in  development  at  different  seasons,  together  with  the  average  daily 
mean  temperatures  prevailing: 

Table  II. — Duration  of  the  egg  stage  of  the  Argentine  ant  at  different  seasons — worker. 


Record  No. 

From—                To— 

Days.1 

Average 
daily 
mean 
tempera- 
ture 
during 
period. 

Average 
daily 
mean 

humid- 
ity. 

1 

Oct.      1,1907 
Dec.  22,1907 
Mar.   14,1908 
May     1,1908 

Julv   20.1908 

Nov.  15,1907 
Feb.  14,1908 
Apr.     9. 1908 
May   23.190S 
Ansr.  10.1908 

45.^ 

55 

27 

23 

22 

19 

19 

12 

°F. 
(2) 
(2) 

70.3 

74 

81 

81 

81.1 

82.5 

Per  ant. 

3   

4 

70  2 

6   

68  9 

7   

82.9 

8   

July    25.190s      Ans?.  12.1908 

81  5 

12   

June  30.1908 
Julv    24,1909 

July   IS,  1908 
Aug.     5,1909 

74  9 

14   

7S  S 

1  Average  days,  27.8. 

2  Cages  kept  in  office;  record  of  exact  temperatures  not  available.  The  balance  of  the  records  were  made 
in  the  "formicarium"  and  the  recording  instruments  kept  in  the  same  room  with  the  cages;  hence  the 
temperature  and  humidity  records  are  correct  for  the  exact  location  of  the  eggs  under  observation. 


40  THE   ARGENTINE   ANT. 

THE    LARVA. 
(PL  IV,  B,  C.) 

The  larva  when  first  hatched  is  not  distinguishable  from  the  esrsr 
without  the  assistance  of  a  magnifying  glass.  For  a  time  after 
hatching  the  body  is  considerably  curved,  the  cephalic  end  being 
almost  in  touch  with  the  caudal  end,  but  as  development  progresses 
the  larva  assumes  more  and  more  of  a  straight  form.  The  curvature 
is  not  entirely  lost,  however. 

A  recently  hatched  larva,  measured  with  the  compound  microscope 
and  eyepiece  micrometer,  was  0.49  mm.  long  by  0.32  wide.  The  fully 
grown  larvae  (workers)  average  1.7  mm.  long  by  0.66  mm.  wide.  The 
largest  one  under  our  observation  measured  1.87  mm.  by  0.765  mm. 

With  the  exception  of  slight  constrictions  of  the  body,  the  larvae 
are  incapable  of  motion,  thus  being  entirely  helpless  and  relying 
altogether  upon  the  ministrations  of  the  attendant  worKers.  The 
latter,  however,  perform  their  duties  faithfully,  and  care  for  their 
charges  with  the  greatest  solicitude.  They  feed  and  groom  the 
young  larvae  continually  and  transport  them  from  place  to  place 
whenever  necessary.  In  case  of  danger  their  first  instinct  appears  to 
be  to  remove  the  young  to  a  place  of  safety,  and  they  readily  sacrifice 
their  own  lives  in  order  to  accomplish  this. 

The  larvae  are  fed  often  by  the  attending  workers  upon  regurgitated 
and  presumably  predigested  food.  There  is  nothing  in  the  appear- 
ance or  actions  of  the  workers  which  do  the  feeding  to  indicate  that 
they  are  different  from  those  which  perform  other  duties,  or  that 
they  are  assigned  to  the  particular  and  exclusive  duty  of  being  nurses. 
The  feeding  of  the  larvae  has  several  times  been  observed  under  a 
magnifying  glass,  and  is  as  follows:  The  larva  ordinarily  lies  upon 
its  side  or  back.  The  attending  worker  approaches  from  any  con- 
venient direction,  usually  from  one  side  or  from  the  direction  in  which 
the  head  of  the  larva  lies,  and,  spreading  her  mandibles,  places  them 
over  the  mouth  parts  of  the  larva,  which  are  slightly  extruded.  The 
tongue  of  the  worker  is  also  in  contact  with  the  larval  mouth.  While 
the  worker  holds  the  body  and  mandibles  stationary  a  drop  of  light- 
colored,  almost  transparent  fluid  appears  upon  her  tongue.  This 
fluid  disappears  within  the  mouth  of  the  larva,  but  it  can  not  be  ascer- 
tained to  what  extent  the  larval  mouth  parts  are  moved  during  the 
operation,  as  they  are  obscured  from  view  by  the  mandibles  and  head 
of  the  attending  worker.  Slight  constrictions  of  the  larval  abdomen 
during  feeding  are  sometimes  noticeable,  at  other  times  not.  The 
time  required  for  feeding  a  single  larva  varies  from  3  to  30  seconds, 
depending  doubtless  on  the  hunger  of  the  "baby."     The  workers 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  IV. 


•   t 

i   • 


Immature  Stages  of  the  Argentine  Ant.    (Original.) 

A,  egg*:  B.  larvae  and  worker  pup*:  C.  larvae,  more  enlarged:  D.  pupa?  of  workers:  at  center, 
male  pupa.    All  enlarged.     (Senior  author's  illustration.) 


LIFE   HISTORY.  41 

proffer  food  to,  or  at  least  inspect,  each  larva,  for  the  worker  doing 
the  feeding  will  place  her  mandibles  to  the  mouth  of  one  larva  after 
another,  feeding  those  which  seem  to  require  it. 

Both  larvae  and  pupae  are  groomed  or  licked  with  the  tongues  of  the 
workers;  thus  they  are  ever  kept  in  a  state  of  absolute  cleanliness. 

The  most  pronounced  increase  in  size  of  the  larvae  occurs  during  the 
first  five  days  after  hatching.  As  is  the  case  with  other  ants,  nothing 
is  voided  from  the  alimentary  canal  during  the  larval  period,  the 
undigested  portions  of  the  food  being  retained  in  the  stomach,  the 
latter  having  no  open  connection  with  the  intestine.  As  the  larva 
reaches  its  full  growth  this  meconium,  or  mass  of  undigested  material, 
becomes  quite  large  and  is  distinctly  visible  as  a  dark  object  in  the 
posterior  portion  of  the  body.  At  about  this  time  communication  is 
established  between  stomach  and  intestine  and  the  meconium  is 
voided.  The  larva  then  enters  the  prepupal  or  semipupal  stage. 
While  the  insect  in  this  stage  is  not  very  different  in  appearance  from 
a  full-grown  larva,  close  examination  shows  a  number  of  slight  differ- 
ences. Aside  from  the  absence  of  the  meconium,  the  cephalic  and 
thoracic  regions  become  markedly  smooth  and  shining,  with  segmen- 
tation very  indistinct,  while  the  segmentation  in  the  abdominal 
region  is,  if  anything,  more  pronounced  than  before.  The  line  of 
demarkation  between  abdomen  and  thorax  is  now  in  evidence,  but 
without  any  very  noticeable  constriction.  The  mouth  parts  are 
protruded  more  than  hi  the  larva.  The  difference  in  appearance 
between  larval  and  prepupal  stages  is  not  great  but  is  sufficient  to 
enable  one  to  predict,  with  reasonable  accuracy,  the  approaching 
transformation  to  the  pupal  stage  proper. 

In  the  later  portion  of  the  larval  stage  we  have  first  been  able  to 
distinguish  between  the  males  and  workers.  The  male  larvae  grow 
to  a  somewhat  larger  size  than  do  the  worker  larvae,  and  it  is  thus 
possible  to  predict  with  some  degree  of  certainty  which  of  grown 
larvae  will  transform  to  males  and  which  to  workers.  In  all  other 
respects,  however,  they  are  apparently  alike.  The  larval  stage  of  the 
queen  is  unknown  to  us. 

DURATION    OF  THE   LARVAL   STAGE. 

The  duration  of  the  larval  period  has  been  determined  by  observa- 
tion in  the  artificial  nests  in  the  same  manner  as  the  incubation  period 
already  described. 

The  following  table  shows  the  duration  of  the  larval  period  at  dif- 
ferent seasons. 


42 


THE    ARGENTINE   ANT. 


Table  III. — Duration  of    larval  stage  of    the  Argentine  ant  at  different    seasons — 

worker. 


Record  No. 

From— 

To— 

Days.1 

Average 
daily 
mean 

tempera- 
ture 
during 
period. 

A  verage 
daily 
mean 

humid- 
ity. 

1 

Nov.  16,1907 
Feb.     5,1908 
do 

Jan.    15,1908 
Apr.     1,1908 
...do 

61 
57 
57 
43 
27 
15 
14 
14 
15 
11 

°  F. 
52.2 
62.2 
62.2 
62 
67 

76.6 
76.1 
80.5 
81.7 
81.1 

Per  cent. 

0 

71  9 

8 

71.9 

10 

Feb.  15,1908 
Feb.  29,1908 
Apr.  10,1908 
Apr.  12,1908 
July   19,1908 
Aug.  13,1908 
Sept.    4,1908 

Mar.  28,1908 
Mar.  20,1908 
Apr.  24,1908 
Apr.  25,1908 
Aug.     1,1908 
Aug.  27,1908 
Sept.  14,1908 

72 

3 

73 

9 

7 

75.2 

2 

82 

11 

71.7 

4 

73.6 

i  Average  days,  31.4. 


THE    PUPA. 

When  the  pupal  stage  is  reached  by  the  young  ant  all  doubt  is 
removed  as  to  the  sex  of  the  individual,  for  one  can  tell  at  a  glance 
which  pupas  will  transform  into  adult  workers,  which  to  males,  and 
which  to  queens.  The  pupae  of  these  three  forms  are  easily  distin- 
guishable and  will  be  discussed  in  the  order  named. 

THE    WORKER    PUPA. 

(PI.  IV,  B,  D.) 

The  worker  pupa  immediately  after  transformation  from  the  larval 
stage  is  pure  white,  without  markings,  except  that  the  compound  eyes 
are  prominent  as  jet-black  spots  upon  the  head.  The  pupa  is 
slightly  larger  than  the  grown  larva,  the  average  length  being  about 
2  mm.  The  head  is  by  far  the  most  prominent  portion.  A  pupa 
measuring  2.04  mm.  in  length  was  found  to  have  a  head  1.19  mm.  in 
length  (dorso-ventral  diameter),  while  the  thorax  and  abdomen 
measured  0.51  and  0.561  mm.,  respectively. 

As  time  for  transformation  to  adult  approaches  the  pupa  changes  to 
a  creamy  color,  then  through  a  light  brown  to  a  dark  brown,  the  latter 
shade  being  almost  as  dark  as  the  body  color  of  mature  workers.  The 
time  of  these  changes  varies  with  the  duration  of  the  pupal  stage,  but 
the  following  record  of  changes  in  color  of  a  pupa  which  occupied  a 
full  20  days  from  larva  to  adult  (callow),  is  near  the  average: 

First  to  seventeenth  day — Pupa  pure  white,  except  compound  eyes. 
Eighteenth  day — Turned  to  a  light  creamy  yellow. 
Nineteenth  day — Became  a  light  brown. 
Twentieth  day — The  brown  color  deepened. 
Twenty-first  day — Reached  teneral  stage. 


LIFE    HISTORY. 


43 


In  some  colonies  there  is  more  or  less  of  an  indistinct  sorting  of  the 
immature  stages,  pupae  being  placed  in  one  portion  of  the  nest  and 
larvae  in  another.  This  tendency  is  not  perceptible  in  many  colonies 
and  is  usually  most  noticeable  in  very  large  colonies. 

The  duration  of  the  pupal  stage  has  been  determined  in  the  manner 
already  described  for  the  incubation  and  larval  periods.  The  range 
of  pupal  development  is  shown  in  the  following  table: 

Table  IV. — Duration  of  pupal  stage  of  the  Argentine  ant,  individual  workers.  1908-9. 


Record  No. 

From— 

To— 

Days.1 

Average 
daily 
mean 
tempera- 
ture 
during 
period. 

Average 
daily 
mean 

humid- 
ity. 

1     

Jan.    21,1908 
Mar.   14,1908 
Mar.  26,1908 
Mar.  30,1908 
Apr.     5,1908 
do 

Feb.   14,1908 
Mar.  27,1908 
Apr.  11,1908 
Apr.  14,1908 
Apr.   15,1908 
Apr.  18,1908 
Apr.  20,1908 
Apr.  23,1908 
May   13,1908 
May   14,1908 
Aug.  11,1908 
Aug.  16,19*8 
Aue.  20,1908 
Sept.    7,1908 
Apr.   28,1909 
June  22,1909 
July     6, 1909 « 

25 
14 
17 
16 
11 
14 
16 
16 
19 
20. 
11 
11 
11 
11 
24 
10 
12.\ 

°  F. 

56.5 

67.5 

73.8 

73.8 

76 

76.3 

76.7 

76.6 

71 

71.2 

82.2 

83 

82.8 

81.4 

70.1 

82.75 

84.08 

Per  cent. 
68.3 

2                      

71.8 

5                          

68.9 

6                                 

70.2 

3                                

73.5 

10                                

74 

do 

74 

8 

Apr,     8, 1908 
Apr.   25,1908 
do 

74.5 

9 

63.5 

11 

61.4 

4 

Aug.     1,1908 
Aug.     6, 1908 
Aug.  10,1908 
Aug.  28,1908 
Apr.     5, 1909 
June  13,1909 
June  24,1909 

80 

12  

74.8 

13 

70.7 

14 

71 

19 

68.4 

21 

68.75 

22 

76.08 

1  Average  days,  15. 
THE    MALE    PUPA. 

(PI.  IV,  at  center.) 

The  male  pupa  is  fully  50  per  cent  larger  than  the  worker  pupa  and 
has,  by  comparison,  an  enormous  thorax.  The  male  pupae  vary  in 
length  from  2.78  to  3.23  mm.,  with  an  average  length  of  3.04  mm.1 
As  the  average  length  of  the  thorax  alone  is  1.19  mm.,  it  is  at  once 
seen  what  a  relatively  large  part  of  the  body  it  constitutes.  The  male 
pupa  is  shown  in  the  center  of  Plate  IV. 

When  first  transformed  from  the  larval  stage  the  male  pupa  is  pure 
white,  with  exception  of  the  compound  eyes,  which  are  faintly  tinged 
with  brown.  Gradually  the  color  of  the  compound  eyes  deepens  and 
the  ocelli  become  visible  as  minute  dark  spots  upon  the  head.  The 
male  pupa,  like  the  worker  pupa,  passes  through  gradations  of  creamy 
yellow,  light  brown,  and  dark  brown  to  almost  black  before  transform- 
ing-to  the  adult  stage.  The  color  reached  by  the  male  pupa  just  prior 
to  transformation  is  much  deeper  than  that  attained  by  worker  pupae. 
The  males  are  assisted  in  their  transformation  to  the  adult  stage  by 


i  From  measurements  of  10  specimens  by  Mr.  Arthur  H.  Rosenfeld. 


44 


THE    ARGENTINE    ANT. 


the  workers,  and  the  pupal  skin,  or  at  least  a  portion  of  it,  is  worked 
backward  to  the  tip  of  the  abdomen  and  there  shed  entirely.  Within 
a  few  hours  after  transformation  the  wings  of  the  male  become  fully 
expanded.  The  following  table  shows  the  duration  of  the  male  pupal 
stage  at  different  seasons. 

Table  V. — Duration  of  pupal  stage  of  the  Argentine  an  t,  Itt'Iciidual  males,  1908. 


Record  Nc. 

From — 

To— 

Day-.- 

Average 
daily 
mean 
tempera- 
ture 
during 
period. 

Average 
daily 
mean 

humid- 
ity. 

1 

Apr.   11 
Apr.   14 
...do.. 

May     1 

May      4 

do. . 

19.i 
20j 
204 

24 
24 
24 
26 
24 
28 

°  F. 
73.6 
73.6 
73.6 
72.3 
72.3 
72.2 
72.8 
71.8 
70.  5 

Pir  cent. 
69.8 

2 

3 

68.6 

4 

Apr.   17 
... do ... . 

Mav    10 
...do 

May    11 

May   13 
...db.... 

Oct.    21 

67  3 

67.3 

8.  J 

Apr.   18 
...do. . .. 

66.7 

66.5 

5 

Apr.   20 
Sept.  24 

65.8 

67.8 

1  Average  days,  23|. 

The  normal  time  of  appearance  of  the  male  pupae  is  in  the  spring, 
but  the  appearance  of  a  relatively  small  number  in  autumn  is  not 
uncommon.  During  April  and  May  they  are  usually  abundant, 
gradually  disappearing  in  the  latter  part  of  May  and  early  June. 
Only  in  one  case  have  they  been  observed  in  midsummer,  when  three 
or  four  male  pupae  were  found  at  Baton  Rouge,  July  24,  1909,  in  a 
huge  nest  which  contained  thousands  of  immature  stages. 

THE    QUEEN"    PUPA. 

The  pupa  which  is  to  become  a  queen  is  readily  distinguished  from 
the  male  or  worker  pupa  by  its  size,  as  it  is  considerably  larger  than 
the  male  and  more  than  twice  as  large  as  the  worker  pupa.  The 
whole  body  is  more  uniformly  developed  than  in  the  case  of  the  male 
pupa.  The  head  and  thorax  are  not  nearly  so  large  in  proportion  to 
the  rest  of  the  body,  the  abdomen  is  much  larger,  and  the  dividing 
line  between  head  and  thorax  is  much  more  distinct.  Apart  from  its 
size  the  queen  pupa  is  readily  recognized  by  the  presence  of  the  promi- 
nent wing  pads. 

Queen  pupae  have  been  found  only  during  April  and  May.  The 
duration  of  this  stage  has  not  been  worked  out,  as  we  have  not  been 
fortunate  enough  to  secure  larvae  which  would  transform  into  queen 
pupae  in  our  cages.  Considerable  numbers  of  these  pupae  have,  how- 
ever, been  collected  in  the  field  by  the  junior  author  and  have  been 
reared  to  the  adult  stage  in  the  artificial  formicaries,  observations  on 
them  extending  over  a  period  of  two  weeks.     The  queen  pupal  stage 


LIFE    HISTORY.  45 

seems  to  occupy  relatively  more  time  than  is  required  for  the  worker 
pupal  stage,  but  the  gradual  change  in  color  from  pure  white  to 
brown  is  about  the  same.  It  seems  probable  that  the  queen  pupal 
stage  extends  over  three  or  four  weeks,  depending  upon  the  prevailing 
temperature.  As  many  as  35  queen  pupae  were  collected  from  one 
colony  in  Audubon  Park,  New  Orleans,  La.,  on  April  29,  1910;  hence 
there  is  every  reason  for  believing  that  the  virgin  queens  are  reared  in 
large  numbers. 

Reasoning  from  what  is  known  concerning  the  development  of 
queens  in  the  case  of  such  insects  as  the  honey  bee,  one  would  expect 
to  find  the  queen  ant  developed  from  the  same  kind  of  an  egg  that 
produces  the  worker  and  that  the  queen  would  be  developed  as  a  result 
of  special  food  given  to  the  female  larva.  It  is  possible  that  the  diet 
furnished  to  our  colonies  in  confinement  did  not  contain  the  requisite 
materials  out  of  which  the  workers  could  elaborate  a  food  suitable 
for  rearing  queens,  and  this  may  account  for  their  failure  ever  to  appear 
in  t-he  artificial  formicaries,  no  matter  how  populous  the  latter  were. 

THE    CALLOW    OR   TENERAL    STAGE. 

During  the  last  few  hours  of  the  pupal  stage,  in  all  forms,  the  legs, 
mouth  parts,  and  antennae  become  more  prominent  and  the  pupa  is 
assisted  in  its  transformation  by  the  workers,  who  attempt  to 
straighten  out  the  legs  and  antennae.  We  are  convinced  that  there 
is  a  very  thin  transparent  membrane  or  skin  surrounding  the  pupa, 
which  is  shed  at  time  of  transformation,  but  its  existence  is  difficult 
to  establish  satisfactorily. 

Immediately  after  transformation  the  young  ant  is  colorless,  almost 
transparent,  but  is  otherwise  identical  in  appearance  with  fully 
mature  specimens.  To  this  stage,  following  the  custom  of  some 
authors,  we  apply  the  term  "  callow."  The  callow  is  at  first  very 
clumsy  and  walks  with  uncertain  steps  and  staggering  gait,  reminding 
one  much  of  a  worker  bee  just  emerged  from  the  brood  comb.  During 
this  stage  the  workers  seem  still  to  feel  a  responsibility  for  the  cal- 
low's welfare,  for  when  the  colony  is  disturbed  the  callows,  like  larvae 
and  pupae,  are  unceremoniously  grabbed  up  by  the  workers  and 
hustled  to  a  place  of  safety. 

The  body  of  the  callow  deepens  in  color  quite  rapidly  and  in  from 
48  to  72  hours  after  transformation  from  the  pupa  becomes  indistin- 
guishable from  that  of  other  adults. 

TIME    REQUIRED   FOR    COMPLETE    DEVELOPMENT. 

By  adding  together  the  minimum  periods  required  for  the  develop- 
ment of  worker  eggs,  larvae,  and  pupae,  as  given  in  Tables  II,  III, 
and  IV,  we  find  that  at  least  33  days  are  required  for  development 


46  THE   AKGENTINE   ANT. 

from  egg  to  adult,  and  in  a  similar  manner  addition  of  the  maximum 
periods  gives  141  days  as  the  maximum  time  required. 

From  the  tables  also  it  is  seen  that  the  average  period  of  incuba- 
tion of  the  eggs  is  28  days,  for  development  of  the  larvae  31  days, 
and  for  maturing  and  transformation  of  pupa  to  adult  15  days. 
By  adding  together  these  averages  we  arrive  at  74  days  as  the  average 
period  of  development.  This,  of  course,  can  not  be  termed  the  time 
required  for  the  development  of  a  generation,  since  workers  do  not 
reproduce,  and  the  term  "generation"  can  be  used  only  in  referring 
to  the  succession  of  queens. 

The  time  required  for  complete  development  of  males  is,  of  course, 
still  unknown,  for  male  larvae  could  not,  in  their  earlier  stages  of 
growth,  be  distinguished  from  the  worker  larvae;  while  the  larval 
form  of  the  queen  is  still  unknown. 

THE    ADULTS. 

There  are  only  three  adult  forms  in  the  case  of  this  ant,  namely, 
the  queen,  male,  and  worker.  Of  the  immature  forms  there  are  three, 
egg,  larva,  and  pupa,  of  each  the  queen,  male,  and  worker.  There  is 
hardly  sufficient  difference  between  the  virgin  queen  and  the  dealated 
queen  after  fertilization  to  justify  considering  them  as  distinct 
forms.  A  complete  colony  may  therefore  consist  of  a  queen  and 
workers  only,  of  queens  and  workers,  or  of  a  queen  (or  queens), 
males,  and  workers.  With  each  of  these  combinations  may  be  asso- 
ciated any  one  or  more  of  the  three  immature  stages,  corresponding 
to  each  of  the  three  adult  forms,  or  nine  immature  stages  in  all. 
Plate  II  shows  a  colony  consisting  of  1  queen,  about  100  workers, 
and  about  20  eggs,  with  no  larvae,  pupae,  or  males  present.  For  a 
technical  description  of  these  adult  forms  the  reader  is  referred  to 
other  pages.     The  following  descriptions  are  general  in  their  nature: 

The  Worker. 

The  worker  measures  from  2.25  to  2.75  mm.  in  length  and  is  well 
illustrated  at  b,  figure  6.  As  with  the  queen,  the  abdomen  extends 
to  about  the  tarsi  of  the  hind  legs  when  the  worker  is  active  or  engaged 
in  feeding.  The  abdomen  is  capable  of  considerable  distension,  and 
when  the  worker  is  fully  engorged  with  sirup  or  other  liquid  its 
chitinous  plates  are  forced  apart,  rendering  the  connecting  mem- 
branes distinctly  visible.  The  writer  has  often  noticed  workers 
returning  from  their  attendance  upon  plant  lice  with  abdomens  so 
distended  that  they  looked  like  little  drops  of  silvery  liquid.  Par- 
ticularly is  this  appearance  presented  when  the  returning  workers 
are  viewed  with  a  strong  light  beyond  them. 


LIFE    HISTOEY.  47 

As  would  naturally  be  expected  in  the  case  of  so  small  a  creature, 
the  weight  of  a  single  worker  is  very  small.  To  determine  it,  1,000 
workers,  freshly  captured  and  killed  with  cyanid  fumes,  were  care- 
fully counted  and  weighed  on  an  analytical  balance.  The  thousand 
insects  weighed  0.2077  gram,  which  gave  the  average  weight  of  each 
worker  as  0.0002077  gram,  or  two-tenths  of  a  milligram. 

As  already  stated,  there  is  only  one  caste  among  the  workers.  In 
a  large  colony  there  seems  to  be  something  of  a  division  of  labor, 
certain  ones  engaging  in  foraging,  others  in  nursing,  and  still  others 
in  excavating  or  sanitary  work.  However,  any  individual  worker 
can  assume  the  duties  of  any  other,  and  does  do  so  when  exigencies 
demand.  Worker  callows,  barely  hardened  into  mature  adults,  go 
forth  in  search  of  food  and  the  hardened  veterans  of  many  months' 
service  seem  to  make  as  efficient  nurses  as  even  the  youngest. 

LENGTH    OF   LIFE. 

The  workers  are  particularly  long  lived.  A  colony  of  about  70 
workers  was  made  queenless  and  broodless  on  July  8,  1908.  By 
October  10  the  number  of  workers  had  become  reduced  to  about  40, 
and  some  of  the  original  ones  survived  until  February  25,  1909,  a 
period  of  6J  months.  As  this  colony  was  queenless,  the  workers  in 
it  were  not  under  normal  conditions.  With  a  queen  present  it  is 
ordinarily  impossible  to  ascertain  the  length  of  life  of  individual 
workers,  owing  to  the  constant  maturing  of  young.  However,  in 
one  case  we  had  opportunity  to  observe  the  survival  of  workers  with 
queen  present  and  with  immature  stages  absent.  A  colony  started 
on  October  10,  1908,  proved  to  have  an  infertile,  dealated  queen 
and  was  kept  under  observation  to  see  how  long  the  workers  would 
survive.  The  last  of  these  died  on  July  22,  1909,  having  lived  for  9 
months  and  12  days  after  their  capture.  Their  age  at  the  time  they 
were  confined  in  the  cage  on  October  10  was,  of  course,  unknown;  but 
it  appears  safe  to  conclude  that  under  normal  conditions  the  workers 
not  infrequently  live  to  an  age  of  at  least  10  or  12  months. 

Mr.  G.  D.  Smith  was  successful  in  keeping  a  queen  and  several 
workers  for  more  than  two  months,  during  which  time  they  had  no 
food  other  than  that  which  may  have  been  contained  in  the  drinking 
water  furnished  them.  During  this  period  of  prolonged  fasting  the 
queen  even  deposited  eggs,  some  of  which  hatched  into  larvae. 

The  Male. 

The  appearance  of  the  adult  male  is  illustrated  at  a,  figure  6.  The 
males  average  about  2.8  to  3  mm.  in  length.  The  most  noticeable 
feature  about  them  is  the  manner  in  which  the  thorax  is  enormously 
developed.     The  abdomen  is  relatively  small  and  the  head  short 


48  THE   ARGENTINE    ANT. 

and  blunt.  The  shape  of  the  head  alone  permits  distinction  between 
the  male  and  virgin  (winged)  queen  without  the  aid  of  a  glass. 

The  normal  time  of  appearance  of  the  males,  of  course,  follows  the 
appearance  of  the  male  pupae,  usually  in  the  spring,  but  a  few  appear 
in  the  fall.  They  are  plentiful  in  the  colonies  during  the  latter  part 
of  April  and  May,  and  numbers  are  still  to  be  found  in  June.  After 
the  beginning  of  July,  however,  they  vanish,  and  are  very  seldom 
seen  during  the  hot  months  of  the  summer.  A  few  are  occasionally 
found  during  October,  November,  and  December,  and  in  one  case 
a  few  males  were  found  in  a  colony  as  late  as  January. 

The  males  are  essentially  drones,  and  never  exhibit  any  indications 
of  industry  or  usefulness  beyond  their  special  function. 

The  Queen. 

Adult  queens  are  found  in  two  forms,  the  winged  and  the  wingless 
or  dealated.  The  former  is  the  virgin  queen  and  the  latter  the  fertile 
or  egg-laying  queen. 

THE    VIRGIN    QUEEN. 

When  the  queen  reaches  maturity  she  possesses  long  narrow  wings 
which  are  rather  opaque,  gray  in  color,  with  the  veins  and  stigma 
pale  brown.  In  other  respects  she  does  not  differ  in  appearance 
from  the  dealated  queen,  described  on  page  49.  The  wings  are 
retained  until  after  the  queen  has  mated.  Mating  may  take  place 
during  the  nuptial  flight  in  spring,  but  under  some  circumstances 
occurs  within  the  nest  without  any  flight  being  made.  In  the  latter 
case  the  queen  loses  her  wings  shortly  after  fertilization  and  assumes 
her  egg-laying  duties  in  the  home  nest  along  with  the  older  queens 
already  there. 

The  earliest  date  at  which  we  were  able  to  find  virgin  queens  in  the 
outdoor  colonies  was  April  1.  Normally  the  first  spring  appearance 
of  males  precedes  the  first  appearance  of  virgin  queens  by  about 
three  weeks. 

Probably  owing  to  the  extreme  shortness  of  the  winged  stage, 
winged  queens  are  very  hard  to  find  in  the  outdoor  nests.  Although 
they  must  exist  in  large  numbers  every  spring,  they  have  been  col- 
lected only  occasionally.  Most  of  our  observations  have  been  made 
upon  specimens  reared  from  pupae  in  artificial  nests. 

An  enormous  and  general  flight  of  males  and  virgin  queens  was 
observed  at  Baton  Rouge,  La.,  in  the  spring  of  1908,  when  large  num- 
bers of  both  sexes  were  captured  in  butterfly  nets.  On  the  other 
hand,  during  the  spring  of  1910  and  that  of  1911  no  general  flight 
was  observed  at  New  Orleans,  La.,  although  close  watch  was  kept  for 
one.  Considerable  numbers  of  males  were  seen  flying  around  the 
city  electric  lights,  and  individual  males  were  found  flying  aimlessly 


LIFE    HISTORY.  49 

in  various  localities,  but  no  queens  were  found  with  them,  and  no 
flight  took  place  that  could  compare  with  the  one  noted  at  Baton 
Rouge  in  1908. 

At  the  same  time  a  large  number  of  queen  pupas  transformed  into 
winged  queens  in  a  large  Janet  style  nest  in  the  laboratory  at  Audu- 
bon Park,  New  Orleans,  La.  About  an  equal  number  of  males  were 
also  present  in  the  same  nest,  which  the  junior  author  watched 
closely  for  a  flight.  Nothing  of  the  kind  took  place.  On  two  occa- 
sions all  ants  were  driven  out  of  the  nest — workers,  males,  and  queens — 
to  see  if  they  could  be  induced  to  fly,  but  after  wandering  around  for 
a  time  they  all  returned  to  the  nest.  The  males  could  be  seen  actively 
pursuing  the  young  queens  inside  of  the  nest,  and  although  copulation 
was  never  actually  observed,  it  must  have  taken  place.  In  the  course 
of  time  all  the  queens  lost  their  wings  and  commenced  to  lay  an 
enormous  number  of  eggs.  These  eggs  hatched,  and  finally  developed 
into  workers,  proving  that  they  were  fertile.  The  males  all  died  one 
by  one,  the  last  one  disappearing  when  about  two  months  old.  It  is 
therefore  evident  that  the  nuptial  flight  is  not  a  necessity. 

Under  natural  conditions  the  tendency  toward  a  general  flight  may 
be  partially  controlled  by  the  comparative  numbers  of  males  and 
young  queens  in  the  nests  and  colonies.  The  weather  conditions 
about  flying  time  may  also  exercise  a  very  important  influence  upon 
the  flying  impulse;  cool,  cloudy,  and  rainy  weather  tending  to 
restrain  the  inclination  to  flight,  and  warm,  clear  weather  encouraging 
it.  The  severity  of  infestation  may  also  be  an  important  factor,  as 
the  ants  would  be  more  likely  to  fly  in  crowded  communities  than  in 
localities  where  they  are  comparatively  scarce. 

The  males  are  much  more  given  to  flight  than  the  virgin  queens. 
In  the  formicarium  at  Baton  Rouge  males  were  often  found  flying 
during  their  season,  and  seemed  to  have  no  preference  as  to  time  of 
flight.  They  were  found  flying  on  cloudy  days  as  well  as  on  clear 
ones  and  as  frequently  at  night  as  in  the  day. 

THE    DEALATED,    OR    FERTILE,    QUEEN. 

The  dealated  queen  is  illustrated  at  c,  figure  6.  The  dealated 
queen  measures  from  4.5  to  5  mm.  in  length,  and  queens  measuring 
6  mm.  in  length  are  not  uncommon.  It  should  be  remarked  here  that 
during  egg-laying  periods  the  abdomen  is  much  larger  and  longer 
than  shown  in  the  drawing.  Normally  the  abdomen  extends  well  beyond 
the  tarsi  of  the  hind  legs.  Unfortunately,  a  drawing  can  not  show 
the  delicate  silky  pubescence  of  the  queen's  body,  and  in  life  she  is  a 
far  more  beautiful  creature  than  one  would  imagine  from  the  drawing, 
correct  though  the  latter  is  in  anatomical  detail. 
75508°— Bull.  122—13 4 


50  THE   ARGENTINE   ANT. 

The  credit  for  first  discovering  and  recognizing  the  queens  of  this 
species  seems  to  belong  to  Mr.  E.  Baker,  formerly  superintendent  of 
Audubon  Park,  New  Orleans,  and  Prof.  II .  E.  Blouin,  formerly  in 
charge  of  the  Audubon  Park  Experiment  Station. 

The  rate  at  which  the  queen  deposits  eggs  varies  with  the  prevail- 
ing temperature,  and  egg  deposition  is  suspended  entirely  at  low  tem- 
peratures. In  the  artificial  formicaries,  already  described,  the  num- 
ber of  eggs  laid  each  day  varied  from  1  or  2  to  as  many  as  50  or  60. 
Thirty  per  day  is  not  far  from  the  normal  number  in  warm  weather, 
when  the  food  supply  is  abundant.  It  appears  probable,  however, 
that  the  queens  deposit  much  more  rapidly  in  large  colonies,  although 
from  the  nature  of  the  case  this  can  not  be  verified  by  direct  observa- 
tion. Egg  deposition  becomes  Very  slow,  or  ceases  entirely,  in  the 
artificial  formicaries  when  the  daily  mean  temperature  falls  below 
68°  F. 

Practically  all  queens  under  observation  have  shown  a  disposition 
to  suspend  egg  deposition  entirely  for  longer  or  shorter  periods,  even 
when  the  occurrence  of  such  periods  can  not  be  accounted  for  by  low 
temperatures. 

Fertile  queens  confined  in  test  tubes  without  accompanying 
workers  will  often  deposit  a  few  eggs  upon  the  walls  of  the  tubes,  but 
we  have  been  totally  unable  to  get  colonies  established  by  confining 
queens  in  artificial  formicaries  without  workers  accompanying  them. 
This  failure  has  not  been  due  to  any  need  of  workers  to  feed  or  care 
for  the  queen,  since  she  can  feed  herself  from  a  supply  of  honey  or 
sugar  as  readily  as  can  a  worker.  Ordinarily  she  attends  to  her  own 
toilet,  and  it  is  doubtful  whether  she  is  in  reality  "attended"  by  the 
workers  in  the  sense  that  queen  bees  are  attended. 

Fertile  queens  do  not  confine  themselves  to  the  formicaries,  either 
natural  or  artificial.  Isolated  dealated  queens  are  not  infrequently 
found  wandering  about  buildings  by  themselves,  and  while  the  queens 
in  artificial  formicaries  ordinarily  stay  within  the  nest  proper,  they 
have  at  times  been  seen  outside  of  it.  The  finding  of  dealated  queens 
wandering  about,  coupled  with  the  fact  that  workers  readily  accept  a 
queen  from  any  source,  seems  to  indicate  that  new  colonies  may 
sometimes  be  established  in  nature  by  workers  associating  with  such 
wandering  queens. 

The  length  of  life  of  the  queen  has  never  been  determined,  but 
there  is  no  doubt  that  it  extends  over  several  years.  Observations 
have  been  carried  on  with  the  same  queen  for  considerably  over  a  year. 

The  number  of  queens  that  may  be  found  in  a  colony  varies  from 
one  to  several  in  the  summer  nests,  and  may  reach  into  the  hundreds 
in  the  large  winter  colonies.  Queens  never  show  the  least  hostility 
to  each  other  or  to  the  workers. 


THE    COLONY   AS   A   WHOLE.  51 

In  the  laboratory  at  Baton  Rouge  it  was  our  custom  to  put  all  sur- 
plus queens  into  one  colony,  kept  for  the  purpose,  and  leave  them  there 
until  wanted.  As  many  as  several  dozen  queens  were  sometimes  in 
this  colony  at  once,  all  living  peaceably  together,  and  with  the  num- 
ber of  queens  sometimes  exceeding  the  number  of  workers. 

Queens  will  frequently  leave  the  nests  with  the  workers,  and  will  be 
observed  in  the  foraging  trails.  Ten  queens  were  collected  in  30  min- 
utes from  a  large  trail  of  workers  at  New  Orleans,  La.,  during  Jan- 
uary, 1911.  These  were  quite  remote  from  the  nearest  nest.  Any 
colony  will  immediately  accept  a  strange  queen  without  hesitation, 
and  it  is  probable  that  a  constant  interchange  of  queens  takes  place 
between  different  colonies. 

THE  COLONY  AS  A  WHOLE, 

In  size  the  colonies  may  vary  from  a  dozen  to  many  thousands  of 
individuals  and  the  number  of  queens  present  in  a  colony  may  vary 
from  one  to  many  hundreds.  Although  the  Argentine  ant  is  particu- 
larly aggressive  and  a  hard  fighter  when  coming  in  contact  with  most 
other  species  of  ants,  there  is  no  apparent  antagonism  between  sepa- 
rate colonies  of  its  own  kind.  In  fact,  in  heavily  infested  areas  the  work- 
ers and  queens  are  so  intermingled  that  the  individuality  of  colonies 
is  entirely  lost  sight  of  and  all  colonies  appear  to  become  part  and 
parcel  of  one  enormous  community.  In  this  respect  the  species  may 
be  said  to  have  a  more  perfect  social  organization  than  even  the  honey 
bees,  colonies  of  which  are  very  distinct  and  the  individuals  of  which 
usually  repel  with  alacrity  any  visitor  from  another  colony. 

SEASONAL   HISTORY. 

In  order  to  connect  the  scattered  and  individual  life  histories 
already  given  into  one  united  whole  it  may  be  well  to  take  a  glance  at 
the  changes  which  occur  in  the  ant  colonies  with  the  different  seasons. 

WINTER   COLONIES. 

The  tendency  of  the  Argentine  ants  to  segregate  into  large  winter 
colonies  is  very  pronounced,  and  during  the  winter  small  colonies 
are  very  scarce,  while  nearly  every  protected  situation  will  reveal 
the  presence  of  enormous  colonies.  The  stages  which  are  represented 
in  the  nest  are  queens,  workers,  eggs,  larvae,  and  worker  pupae. 
During  cold  weather  very  few  changes  occur.  The  egg  and  larval 
periods  are  very  much  lengthened  compared  to  the  summer  rate  of 
development.  The  workers  themselves  move  very  little,  and  a  large 
colony  will  subsist  upon  a  small  supply  of  food  for  long  periods. 
During  warm  days  heavy  trails  of  workers  emerge  from  the  nests 
and  carry  back  anything  available  for  food.  Except  for  this  the  ants 
may  be  considered  as  almost  in  hibernation  during  the  winter  months. 


52  THE    ARGENTINE   ANT. 

When  the  temperature  falls  as  low  as  60°  F.  the  ants  become 
sluggish,  and  foraging  is  largely  suspended.  At  from  50°  to  55°  F. 
there  is  practically  no  foraging,  and  when  this  temperature  is  reached 
within  the  nest  all  adult  ants  become  inactive,  moving  only  occasion- 
ally, and  even  then  with  apparent  difficulty.  Activity  is  not  strictly 
limited  by  these  temperatures,  however.  On  one  occasion  we  found 
workers  foraging  in  a  building  the  interior  of  which  was  at  43°  F., 
but  the  colony  itself  was  outside  the  building  and  at  a  higher  tem- 
perature. Very  few  refrigerators  are  cold  enough  to  keep  out  these 
invaders  when  the  outside  temperature  is  warm  enough  for  them  to 
forage  normally.  On  the  very  hottest  days  of  summer  they  will 
enter  refrigerators  and  even  crawl  into  the  ice  chamber  itself  in  order 
to  reach  some  much-desired  delicacy. 

The  most  ideal  location  for  the  large  winter  colonies  is  in  piles  of 
decomposing  vegetable  matter.  This  material  gives  off  a  large  quan- 
tity of  heat  during  the  process  of  rotting  and  consequently  furnishes 
the  ants  with  automatically  heated  apartments.  In  the  same  manner 
in  which  the  ants  seek  optimum  humidity  conditions  during  the 
summer  months,  so  they  will  regulate  their  location  to  preserve  an 
even  temperature  in  their  nests  in  the  winter.  In  cold  weather  they 
will  carry  the  young  stages  toward  the  center  of  the  piles,  while  in 
warmer  weather  they  will  be  found  near  the  surface. 

Of  course  all  the  ants  are  not  able  to  find  ideal  locations  for  the 
winter  months,  and  great  numbers  have  to  locate  themselves  as  well 
as  they  can.  In  open  fields  great  numbers  will  be  found  under  large 
ridges,  or  along  ditch  banks,  particularly  those  which  have  a  southern 
exposure.  Many  will  burrow  into  the  ground  at  the  bases  of  large 
trees,  where  their  tunnels  and  galleries  will  sometimes  attain  a  depth 
of  12  to  14  inches. 

Under  Louisiana  conditions  the  winter  colonies  are  in  evidence 
during  the  months  of  December,  January,  and  February.  The  segre- 
gating tendency  becomes  marked  during  November,  and  the  "divis- 
ional migration"  normally  occurs  in  February,  but  may  not  take 
place  until  March  if  the  spring  is  cold  and  wet. 

SUMMER  COLONIES. 

As  soon  as  the  weather  gets  warmer  in  the  spring  and  food  becomes 
abundant  the  large  winter  colonies  break  up  into  a  great  number  of 
smaller  colonies.  These  usually  consist  of  one  or  more  queens  and  a 
considerable  number  of  workers,  and  they  establish  themselves  in 
any  good  location  where  a  supply  of  food  is  available.  In  places 
where  food  is  exceptionally  abundant  these  summer  colonies  will  still 
remain  very  strong  in  numbers.  Under  large  magnolia  or  oak  trees, 
for  example,  colonies  with  10  or  20  queens  and  many  thousand 
workers  are  nearly  always  present. 


THE    COLONY   AS   A   WHOLE.  53 

A  short  time  after  the  " divisional  migration"  has  taken  place  in  the 
early  part  of  March,  the  large  amount  of  food  brought  in  by  the 
workers,  acting  in  conjunction  with  the  warmer  temperature,  appears 
to  stimulate  the  queens  to  lay  great  numbers  of  eggs.  Most  of  the 
young  stages  carried  through  the  winter  or  which  have  slowly  matured 
during  winter  have  by  this  time  transformed  into  workers,  so  that 
the  colonies  consist  of  many  workers,  with  comparatively  few  imma- 
ture stages  other  than  the  eggs.  Hatching  takes  place  during  the  latter 
half  of  March,  and  the  larvae  resulting  from  these  eggs,  after  develop- 
ing, transform  into  three  classes  of  pupae,  viz,  queen,  male,  and 
worker.  Of  these  the  male  pupae  preponderate,  with  the  workers  a 
close  second  and  queen  pupae  a  very  poor  third.  The  male  pupae 
appear  in  great  numbers  several  days  before  the  queen  pupae  appear, 
which  may  possibly  indicate  a  slightly  longer  larval  period  for  the 
queens  than  for  the  males. 

The  adult  winged  males  appear  during  the  latter  part  of  April  and 
in  May,  and  are  in  evidence  in  the  nests  until  the  beginning  of  June, 
when  they  begin  to  disappear.  The  winged  queens  appear  a  few  days 
later.  For  some  reason  the  winged  queens  are  extraordinarily  diffi- 
cult to  find  in  the  nests,  although  their  large  size  and  long  narrow 
wings  should  make  them  very  conspicuous.  However,  only  three 
winged  queens  have  as  yet  been  located  in  the  nests  under  natural 
conditions  in  Louisiana.  Fortunately  the  queen  pupae  are  not  so 
difficult  to  discover,  and  a  considerable  number  have  been  reared  to 
the  adult  stage  in  Janet  style  nests  in  the  laboratory,  where  most  of 
our  observations  upon  this  stage  have  been  made. 

The  appearance  of  the  winged  queens  and  males  may  or  may  not 
be  followed  by  a  nuptial  flight.  In  either  case,  after  the  queens  have 
become  fertile  they  lose  their  wings  and  immediately  start  laying 
great  numbers  of  eggs.  These  eggs  develop  into  workers,  with  the 
exception  of  a  few  eggs  which  are  laid  in  the  late  autumn  and  develop 
into  males.  It  thus  follows  that  the  most  rapid  and  conspicuous 
increase  in  numbers  occurs  during  July,  August,  and  September, 
when  the  eggs  laid  by  the  army  of  young  queens  complete  their  life 
history  and  transform  into  adult  workers. 

From  then  on  to  late  in  the  fall  the  history  of  the  colonies  is  very 
similar  and  devoid  of  incident.  The  numerical  strength  of  the  ants 
is  constantly  on  the  increase,  and  it  is  probable  that  the  greatest 
natural  dispersion  occurs  during  the  fall  months,  after  the  nests 
have  been  excessively  crowded  by  the  activity  and  increase  of  the 
summer. 

During  the  latter  part  of  October  and  in  November  the  nights 
begin  to  get  cool  and  we  find  the  first  inclination  toward  the  form- 
ation of  the  winter  colonies.  The  nests  in  exposed  open  situations 
are   gradually    deserted,   and    strong    colonies    accumulate    in  well- 


54  THE   ARGENTINE   ANT. 

protected  situations.  This  becomes  more  pronounced  during  the 
latter  part  of  November,  and  in  the  beginning  of  December  we  find 
that  the  winter  colonies  with  which  we  began  are  once  more  restored 
and  that  large  united  colonies  are  the  rule,  with  small  colonies  the 
exception. 

COMPOUND    COLONIES    OR   COMMUNITIES. 

Mention  should  not  be  omitted  of  the  pronounced  manner  in  which 
the  social  habit  is  extended  beyond  the  limits  of  the  individual  nest 
or  formicary.  During  the  summer  season  of  activity,  and  in  heavily 
infested  areas,  communication  between  adjacent  colonies  is  com- 
monly observed.  Not  only  the  workers,  but  even  fertile  queens, 
travel  from  one  colony  to  another.  So  closely  are  adjacent  colonies 
associated  in  their  activities  that  one  can  not  do  otherwise  than  con- 
sider a  heavily  infested  area  as  one  enormous  "compound  colony"  or 
community. 

MIGRATIONS. 

Four  distinct  types  of  migration  are  exhibited  by  these  ants, 
without  including  the  long  trips  which  they  take  in  columns  to  and 
from  the  nests  in  search  of  food. 

GENERAL   MIGRATION    OR   DISPERSION. 

By  general  migration  is  meant  the  slow  but  steady  spread  of  the 
ants  from  infested  points  into  adjacent  uninfested  territory.  This  is 
practically  continuous,  and  while  under  natural  conditions  it  may 
amount  to  only  a  few  hundred  feet  per  year  it  is  greatly  accelerated 
by  artificial  dissemination  of  the  ants  by  man  and  his  agencies. 

MIGRATION   TO   FOOD   SUPPLY. 

When  the  supply  of  food  becomes  scarce  in  the  immediate  vicinity 
of  a  colony  and  a  plentiful  supply  is  discovered  at  a  distance  by  the 
foraging  workers,  movement  of  the  colony  in  toto  to  the  neighbor- 
hood of  the  latter  is  not  infrequent.  Trees  or  plants  harboring  large 
numbers  of  scale  insects  are  invariably  surrounded  by  many  populous 
colonies  and  the  housewife  who  grows  careless,  permitting  the  ants 
to  get  food  in  plenty  within  her  domicile,  is  soon  repaid  by  having 
the  premises  overrun  with  the  pests.  One  can  easily  note  this  form 
of  migration  by  keeping  a  constant  supply  of  honey  or  sirup  in  one 
place  for  several  days  and  providing  a  suitable  nesting  place — such 
as  a  decaying  log — near  it.  The  latter  is  shortly  occupied  by  one  or 
more  colonies. 

CONCENTRATING   MIGRATION. 

Concentrating  migration  takes  place  within  the  infested  territory 
and  consists  of  the  coming  together  of  a  large  number  of  smaller  colo- 
nies to  form  a  single  large  colony.     This  migration  occurs  under 


THE   COLONY   AS   A   WHOLE.  55 

various  adverse  conditions.  During  floods  the  ants  will  concentrate 
in  great  numbers  upon  elevated  ground,  or  many  colonies  will  carry 
their  young  stages  up  the  same  tree  in  order  to  get  protection  from 
the  rising  water.  The  most  pronounced  concentration,  however, 
occurs  at  the  approach  of  cold  weather  in  the  fall,  when  large  numbers 
of  colonies  concentrate  at  one  point  to  form  the  large  winter  colonies, 
often  consisting  of  hundreds  of  queens  and  many  thousands  of  work- 
ers.    These  colonies  are  fully  described  elsewhere. 

DIVISIONAL   MIGRATION. 

Divisional  migration  is  the  opposite  of  concentrating  migration, 
and  is  always  in  evidence  after  a  large  number  of  ants  have  concen- 
trated at  one  place.  It  is  most  conspicuous  in  the  spring,  when  the 
large  winter  colonies  break  up  into  a  great  number  of  smaller  ones. 
These  small  colonies  usually  consist  of  one  or  more  queens  and  a  sup- 
ply of  workers.  They  distribute  themselves  in  all  directions  from  the 
large  colony,  and  locate  hi  any  place  which  affords  suitable  protec- 
tion and  an  available  food  supply. 

NESTS    OR    NATURAL    FORMICARIES. 

Almost  any  place  seems  to  be  suitable  for  the  location  of  nests  of 
the  Argentine  ant,  provided  that  light  and  water  may  be  sufficiently 
excluded.  Some  of  the  situations  in  which  they  have  been  found 
are  within  hollow  trees,  beneath  the  rough  bark  of  growing  trees, 
in  forks  of  trees,  in  rubbish  and  compost  heaps,  in  decaying  logs  and 
timbers,  beneath  boxes  and  boards,  under  and  in  brick  foundations, 
in  stored  household  goods,  beneath  shingles  on  roofs,  in  rolls  of  wrap- 
ping paper,  between  walls  of  dwellings,  in  flowerpots,  in  piles  of 
brick  and  stove  wood,  in  garbage  cans,  in  bags  of  sugar,  in  birds' 
nests,  in  discarded  tin  cans,  in  moss  packing  about  the  roots  of  nur- 
sery stock,  and  in  straw  packing  containing  glassware  or  china,  in 
beehives  with  colonies  of  bees,  under  discarded  tin  roofing,  around 
the  roots  of  cotton,  corn,  sugar  cane,  and  other  growing  crops,  in 
railway  cars,  in  various  places  on  river  steamboats  and  ocean-going 
vessels,  in  old  clothes,  under  street-car  tracks,  under  brick  and  con- 
crete pavements,  in  greenhouse  benches,  inside  the  husks  of  roasting 
ears,  inside  of  cotton  bolls,  in  hollow  iron  electric -light  posts,  in  the 
cracks  and  crevices  in  telephone  and  telegraph  poles,  and  in  the  cinder 
ballast  of  railroad  tracks. 

Most  of  the  situations  named  are  used  as  permanent  nesting  places 
so  long  as  weather  conditions  do  not  force  the  ants  to  find  more 
suitable  quarters.  With  the  advent  of  unfavorable  conditions  the 
ants  move  their  colonies  with  alacrity. 


56  THE   ARGENTINE   ANT. 

Many  permanent  nests  are  located  in  the  tops  of  trees,  in  rotten 
branches,  or  in  places  where  borers  or  termites  have  been  working. 

In  rotten  logs  the  ants  will  nearly  always  utilize  old  borer  or  termite 
tunnels  for  their  nests,  but  do  not  appear  to  do  any  boring  for  them- 
selves. 

The  facility  with  which  entire  colonies  move  is  sometimes  amazing. 
If  a  nest  is  disturbed  the  workers  will  frequently  move  all  stages  and 
establish  another  nest  in  a  fresh  location  in  the  course  of  a  very  few 
minutes. 

UNDERGROUND   NESTS. 

The  ants  seldom  burrow  to  any  great  depth  in  the  ground.  The 
exceptions  to  this  occur  during  hot,  dry  weather  in  the  summer  or 
during  particularly  cold  spells  in  the  winter.  In  the  dry  spells  they 
evidently  work  downward  in  an  endeavor  to  secure  sufficient  hu- 
midity for  the  young,  while  in  the  wintertime  they  sometimes  go 
deep  into  the  soil  for  the  sake  of  protection  from  the  cold.  The 
deepest  burrows  which  we  have  measured  have  been  14  inches  in 
depth,  but  they  usually  average  from  4  to  10  inches  under  normal 
conditions.  These  deep  burrows  are  usually  located  at  the  foot  of 
tree  trunks,  or  under  the  ridges  in  cane,  cotton,  or  corn  fields. 

Under  more  favorable  circumstances,  however,  the  underground 
galleries  average  from  1  to  4  inches  in  depth.  In  summer  time  the 
ants  appear  to  do  as  little  excavating  as  possible  and  seem  to  limit 
their  efforts  to  excluding  light  and  water.  When  the  nests  are 
located  above  ground,  under  boxes,  boards,  stones,  etc.,  very  little 
soil  is  used,  and  this  is  utilized  in  closing  holes,  etc.,  to  keep  out 
light  and  drafts. 

WET-WEATHER   NESTS    OR   SHEDS. 

In  wet  situations  or  after  heavy  rains,  when  the  ground  has  become 
soaked  with  water,  the  ants  construct  curious  honeycombed  structures 
around  the  bases  of  tree  trunks.  These  are  made  of  a  great  number 
of  fine,  loose  particles  of  soil,  usually  supported  by  grass  stems  or 
loose  leaves.  They  vary  from  one-half  inch  to  as  much  as  5  inches 
in  height,  and  sometimes  cover  an  area  of  several  square  feet.  They 
are  built  with  great  rapidity  by  the  workers,  and  are  extremely  frail, 
falling  in  at  the  lightest  touch.  As  a  result  of  this  weakness  these 
nests  disappear  after  a  few  days  of  dry  weather,  or  are  washed  away 
by  showers.  They  consist  of  a  maze  of  covered  galleries,  in  which 
large  numbers  of  the  larvae  and  pupae  are  placed.  Their  purpose 
appears  to  be  to  afford  protection  to  the  young  stages  until  the 
ground  gets  dry  enough  for  the  underground  galleries  to  be 
reoccupied,  or  they  may  be  used  to  dry  and  "air"  stages  which 
have  become  wet,  the  loose  construction  permitting  a  liberal  circula- 
tion of  the  air  through  the  walls  and  ceilings.     (See  PL  V.) 


Bui.  122,  Bureau  of   Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  V. 


Wet-Weather  Nest  or  Shed,  Erected  by  Argentine  Ants  During  Rainy  Weather. 

(Original.) 


THE   ARGENTINE   ANT.  57 

GENERAL    OBSERVATIONS, 

AVERSION    TO    LIGHT. 

The  ants  demonstrate  in  many  ways  their  dislike  of  light,  or  at 
least  their  aversion  to  it.  Their  nests  are  always  located  in  dark 
places,  the  ants  are  active  all  night,  and  their  immature  stages  are  never 
exposed  to  light  except  for  brief  periods  in  emergencies.  If  the 
opaque  cover  is  removed  from  the  top  of  an  artificial  ant  nest  for  a 
considerable  time,  all  the  ants  will  come  out  and  will  refuse  to  return 
until  the  cover  is  replaced.  Several  experiments  were  made  at 
Baton  Rouge,  La.,  in  1909,  using  different  colored  glasses  for  cage 
covers,  but  the  ants  were  not  satisfied  unless  the  cover  was  absolutely 
opaque.  While  they  will  go  anywhere  into  daylight  in  search  of 
food,  they  will  cover  over  as  thoroughly  as  possible,  with  their 
protective  "sheds,"  the  colonies  of  scale  insects,  mealy-bugs,  and 
aphides  which  they  habitually  frequent. 

SENSE  OF   SMELL. 

The  workers  exhibit  a  very  keen  sense  of  smell  by  the  manner 
in  which  they  locate  certain  foods.  Meat  which  is  wrapped  in  heavy 
wrapping  paper  will  attract  thousands  of  the  insects,  and  they  will 
work  their  way  through  the  various  folds  and  crevices  of  the  paper 
in  a  surprising  manner  until  they  reach  the  meat  itself.  The  workers 
readily  secure  entrance  into  the  ordinary  Mason  or  glass  fruit  jar, 
if  one  omits  placing  beneath  the  cover  the  rubber  ring  or  gasket. 
No  matter  how  tightly  the  cover  is  screwed  on,  the  workers  follow 
the  spiral  threading  between  cover  and  glass  until  the  interior  is 
reached. 

Another  illustration  of  the  sense  of  smell  is  seen  in  the  readiness 
with  which  trails  are  restored  when  broken  or  disturbed.  If  a  line 
of  ants  be  moving  across  a  floor  in  a  circuitous  line,  for  example, 
and  all  ants  be  swept  from  the  floor  with  a  broom,  the  next  on-coming 
workers  will  follow  exactly  the  original  course.  This  may  be  repeated 
indefinitely  and  the  trail  will  always  be  established  in  the  original 
location.  If,  however,  some  strong-smelling  substance,  like  oil  of 
citronella  or  kerosene,  be  placed  upon  the  trail  the  ants  become 
confused  at  once  and  by  their  aimless  wandering  about  show  plainly 
that  they  can  not  locate  the  original  pathway. 

SIGHT. 

While  the  Argentine  ants  are  extremely  sensitive  to  light,  it  is 
doubtful  if  they  possess  the  sense  of  sight.  The  action  of  light  can 
generally  be  described  as  exerting  a  repelling  influence  upon  them 
and  they  avoid  it  as  much  as  they  can.  That  they  do  not  use  eyesight 
in  locating  food  substances  has  long  been  recognized.     Their  trails 


58  THE   AEGENTINE  ANT. 

will  frequently  encircle  the  spot  which  they  ultimately  hope  to  attain. 
They  will  never  attempt  to  avoid  a  hand  threatening  from  any 
direction  as  a  spider  will  do,  but  will  continue  going  ahead  until 
their  antennae  touch  the  obstacle.  The  manner  in  which  they 
religiously  follow  their  trails  and  the  confusion  which  results  when 
these  trails  are  destroyed  proves  that  they  do  not  trust  to  a  sense  of 
sight  in  traveling.  This  is  illustrated  again  by  the  fact  that  they  are 
active  all  night  in  the  darkest  situations. 

HEARING. 

The  sense  of  hearing  in  these  insects  is  not  acute,  even  if  indeed  it 
be  developed  at  all.  The  ants  are  not  disturbed  by  ordinary  noises, 
such  as  talking  or  working  about  the  nests.  If,  however,  one  emits 
a  loud  shout  within  a  few  inches  of  the  formicary,  or  fires  a  pistol 
near  it,  the  ants  are  thrown  into  the  confusion  and  excitement 
characteristic  of  them  when  disturbed.  It  seems  not  impossible 
that  in  such  cases  they  have  detected  actual  vibrations  of  the  surface 
on  which  they  are  located,  due  to  the  action  of  the  sound  waves. 
Strangely  enough,  in  situations  where  loud  noises  and  vibrations  are 
of  constant  occurrence,  the  ants  become  accustomed  to  them.  Thus 
at  New  Iberia,  La.,  we  found  ant  colonies  between  and  under  the 
ties  of  a  railroad  track  over  which  many  trains  passed  daily. 

CANNIBALISM. 

Cannibalism  in  any  form  is  extremely  rare  in  the  case  of  this 
species,  and  true  cannibalism  has  not  yet  been  observed.  The  only 
thing  at  all  approaching  it  was  observed  in  the  case  of  a  colony  kept 
in  our  formicarium,  the  workers  of  which  developed  a  habit  of  eating 
the  eggs  as  fast  as  they  were  deposited  by  the  queen.  This  colony 
was  established  in  an  artificial  formicary  on  November  27,  1907,  and 
from  that  time  until  the  early  part  of  July,  1908,  larvae  were  reared 
more  or  less  continuously  and  in  the  usual  numbers.  In  July  it  was 
noticed  that  the  number  of  immature  stages  became  steadily  smaller, 
and  on  July  28  a  quick  removal  of  the  cover  from  the  cage  disclosed 
several  workers  in  the  act  of  eating  eggs.  Thinking  that  this  might 
be  due  to  lack  of  sufficient  food  of  an  animal  nature  fresh  meat  was 
at  once  furnished  the  colony  and  was  thereafter  kept  continually 
accessible.  In  spite  of  this  the  egg-eating  habit  continued  until 
November  5,  1908,  all  eggs  being  eaten  within  a  few  hours  after  their 
deposition  by  the  queen.  By  this  time  the  number  of  workers  in  the 
colony  had  been  reduced  to  six,  and  by  November  1 1  the  queen  and 
remaining  workers  were  dead,  the  colony  having  apparently  been 
exterminated  through  lack  of  any  maturing  workers  to  replace  those 
dying  from  old  age  and  accident. 


GENEKAL   OBSERVATIONS.  59 


SANITATION. 


All  adult  members  of  the  colony  keep  themselves  scrupulously 
clean,  after  the  manner  of  most  hymenopterous  insects.  Workers 
divest  their  bodies  and  legs  of  foreign  matter  by  persistent  rubbing 
of  the  body  and  antennae  with  their  legs,  while  the  tarsi  are  cleaned 
by  pulling  them  between  the  mandibles.  At  times  we  have  seen  the 
workers  assisting  each  other  in  these  operations,  particularly  when 
some  gummy  or  adhesive  substance  became  attached  to  the  head  and 
mandibles.  On  one  occasion  the  senior  author  observed  one  worker 
industriously  cleaning  the  mandibles  of  a  companion.  During  this 
operation,  which  lasted  for  several  minutes,  the  worker  receiving  the 
kindly  ministrations  stood  with  her  head  well  raised,  mandibles 
extended,  and  feet  firmly  braced,  while  the  teeth  of  her  mandibles 
were  thoroughly  cleaned  by  those  of  her  sister. 

The  queen  is  occasionally  cleaned  and  groomed  by  the  workers, 
but  for  the  most  part  she  attends  to  her  own  toilet,  being  nearly  as 
skillful  and  dextrous  at  the  task  as  are  the  workers  themselves. 
Larva?  and  pupae  are  groomed  from  time  to  time,  this  grooming  being 
done  with  the  tongues  of  the  workers. 

Dead  adults  or  larvae  are  not  tolerated  within  the  colony  and  are 
removed  immediately.  Dead  adults  are  also  invariably  removed 
from  the  vicinity  of  any  food  supply  which  the  ants  are  visiting. 

Decaying  annual  matter  is  not  tolerated  in  near  proximity  to  the 
nests.  If  the  ants  are  unable  to  remove  it  bodily  they  will  carry 
particles  of  earth  with  which  to  bury  it,  much  after  the  manner 
adopted  by  honey  bees  in  covering  with  propolis  any  dead  animal 
which  they  can  not  remove  from  their  hives.  The  following  example 
will  serve  to  illustrate  this  habit:  A  small  minnow,  recently  dead, 
was  placed  near  the  entrance  of  one  of  the  artificial  formicaries.  It 
was  immediately  covered  with  workers,  and  in  the  course  of  a  few 
hours  all  the  soft  portions  had  been  torn  apart  and  carried  into  the 
formicary,  little  remaining  except  the  bones  and  skin.  On  the  fol- 
lowing day  another  fresh  minnow  was  given  the  same  colony.  While 
this  was  torn  apart  the  same  as  the  first  one,  it  did  not  receive  nearly 
as  much  attention.  When  a  third  minnow  was  given  the  colony  the 
workers  paid  no  attention  to  it,  having  evidently  had  fish  "  a  plenty." 
As  soon  as  it  commenced  to  decay  the  workers  brought  particles  of 
trash  and  dirt  from  their  nest  and  piled  these  up  around  the  minnow. 
This  work  they  continued  for  three  days,  by  the  end  of  which  time 
the  remains  of  the  minnow  were  completely  buried.  Decaying  fruit 
left  near  the  artificial  nests  was  treated  in  the  same  manner. 


RATE    OF   TRAVEL. 


One  of  our  associates,  Mr.  G.  D.  Smith,  made  some  interesting 
experiments  to  determine  how  rapidly  the  workers  travel  both  in 
going  to  food  and  in  returning  from  it  with  their  loads.     Sirup  was 


60  THE   ARGENTINE   ANT. 

placed  on  the  comparatively  smooth  floor  of  an  infested  building, 
and  when  the  ants  were  visiting  it  in  large  numbers  a  distance  of 
6  inches  was  measured  off  on  one  of  the  principal  "  trails. "  The  rate 
of  travel  of  individuals  over  this  6  inches  was  then  noted.  Mr.  Smith 
found  that  the  average  time  required  to  travel  the  6  inches  when 
going  to  the  food  supply  was  12+  seconds,  or  at  the  rate  of  29  inches 
per  minute.  When  returning  from  the  food,  presumably  with  their 
stomachs  filled  with  sirup,  the  average  time  required  to  travel  the 
G  inches  was  21  seconds,  or  at  the  rate  of  17  inches  per  minute.  The 
rapidity  with  which  the  foraging  ants  can  travel  (29  inches  a  minute, 
or  145  feet  per  hour)  explains  their  ability  to  keep  thoroughly 
patroled  all  of  the  walls,  furniture,  and  other  contents  of  a  building 
within  their  reach.  It  explains  at  the  same  time  the  reason  for  their 
so  quickly  locating  food  supplies  left  accessible  to  them. 

The  rate  of  travel  over  horizontal  polished  surfaces  is,  however, 
much  greater  than  that  cited  above.  On  a  tiled  floor  or  on  the  top 
of  a  glass  showcase  their  speed  is  two  or  three  times  as  great  as  that 
just  given.  In  fact,  it  is  almost  impossible  to  capture  the  workers 
on  a  tiled  floor,  so  rapidly  do  they  move.  This  same  degree  of  speed 
is  not  attained  on  vertical  polished  surfaces,  such  as  window  panes. 

.       STORAGE    OF   FOOD. 

Only  to  a  very  small  extent  do  the  workers  of  this  species  provision 
their  nests  for  future  emergencies.  They  are  given  to  carrving  let- 
tuce seed,  and  perhaps  other  seeds,  into  their  colonies  at  times,  but 
the  bulk  of  these  seed  are  used  up  in  a  short  time,  and  in  a  few  days  all 
have  disappeared.  Apparently  the  desire  to  carry  in  a  full  supply  of 
any  desirable  food  is  the  cause  for  this  storage,  rather  than  any  fixed 
instinct  toward  providing  the  colony  with  permanent  stores.  In  like 
manner,  when  the  ants  have  access  to  large  amounts  of  granulated 
sugar,  the  granules  are  carried  into  the  nest  and  deposited  in  various 
parts  of  the  galleries,  there  being  no  place  set  aside,  apparently,  as  a 
granary  or  storehouse.  Like  the  seeds  above  mentioned,  the  supply 
of  sugar  is  consumed  within  a  few  hours  or  a  few  days  after  its 
acquisition.  Particles  of  meat  are  deposited  in  the  galleries  in  simi- 
lar manner,  often  to  be  neglected  until  they  are  too  dry  to  be  of  much 
service.  Even  when  dried,  however,  they  seem  to  furnish  a  relish  or 
variation  in  the  diet,  as  workers  may  be  seen,  from  time  to  time, 
rasping  off  small  shreds  with  their  mandibles  and  then  masticating 
these  with  apparent  enjoyment. 

Liquid  food,  such  as  honeydew,  sirup,  etc.,  is  not  deposited  any- 
where in  the  nest,  and  if  any  liquid  food  is  kept  in  reserve  at  all  it  is 
merelv  that  which  is  retained  in  the  stomachs  of  the  workers.     Appar- 


RELATIONS    WITH    OTHER   ARTHROPODA.  61 

ently  liquid  food  is  consumed  soon  after  being  brought  into  the  for- 
micary, as  evidenced  by  the  following  observation: 

Some  fresh  honey  was  placed  upon  the  food  table  of  an  artificial 
formicary,  and  when  the  first  worker  was  observed  to  leave  the  honey 
the  top  of  the  formicary  was  removed  and  her  actions  observed. 
Upon  entering  the  colony  she  was  met  by  three  other  workers,  all 
of  which  placed  their  mandibles  to  hers.  As  she  regurgitated  the 
liquid  they  sipped  it  up.  When  one  of  these  workers  had  received  a 
sufficient  quantity  she  retired  and  another  took  her  place,  as  many 
as  four  or  five  workers  sometimes  feeding  at  once.  The  foraging 
worker  in  this  manner  supplied  about  15  others  with  food,  after 
which,  her  supply  being  apparently  exhausted,  she  left  the  group  of 
assembled  feeders  and  went  her  way,  leaving  some  of  them  hungry 
and  still  unsatisfied. 

RELATIONS  WITH  OTHER  ARTHROPODA. 
FORMICID.E. 

It  may  be  said  in  general  that  the  Argentine  ant  will  not  tolerate 
the  presence  of  other  species  of  ants  within  its  domains.  There  are 
a  few  exceptions  to  this  rule.  In  1908  Mr.  G.  A.  Runner  and  the 
junior  author  found  a  small  colony  of  Monomorium  minimum  Buck- 
ley living  in  the  same  tree  stump  with  a  colony  of  Argentine  ants  at 
Baton  Rouge.  The  Monomorium  colony  possessed  a  number  of  young 
stages  and  appeared  to  be  unmolested  by  the  Argentine  ants.  The 
following  season,  however,  the  Argentine  ants  were  in  full  possession 
of  the  stump,  and  no  trace  of  Monomorium  could  be  found.  During 
the  same  summer  another  small  colony  of  M.  minimum  was  noticed 
living  in  a  fig  tree  in  territory  heavily  infested  with  the  Argentine 
ant.  This  was  also  at  Baton  Rouge.  This  colony  was  observed  for 
several  weeks,  but  finally  died  out,  though  it  could  not  be  determined 
whether  the  Argentine  ants  were  responsible  for  its  annihilation. 

In  another  case  a  log  was  split  open,  disclosing  vigorous  colonies 
of  both  Iridomyrmex  Jiumilis  and  M.  minimum.  Whether  the  ants 
were  occupying  the  same  chambers  or  whether  the  nests  were  in 
close  but  disconnected  chambers  could  not  be  ascertained,  but  the 
Monomorium  workers  were  seen  to  pick  up  and  carry  away  the  larva? 
of  Jiumilis  with  as  much  solicitude  as  they  did  their  own.  Just  what 
relationship  obtains  between  these  two  species  we  have  not  been 
able  to  determine,  but  certain  it  is  that  Jiumilis  tolerates  this  small 
species  to  a  much  greater  extent  than  it  does  any  other  ant.  At 
Baton  Rouge  Monomorium  minimum  still  seems  to  maintain  its 
normal  abundance,  and  this  certainly  can  not  be  said  of  any  other 
species  of  ant. 


62  THE   ARGENTINE   ANT. 

An  account  of  the  methods  used  by  the  Argentine  ants  in  over- 
coming other  species  of  ants  was  published  by  the  senior  author  * 
in  the  Journal  of  Economic  Entomology. 

Prof.  W.  M.  Wheeler,  in  Entomological  News  for  January,  1906, 
gives  an  interesting  account  of  the  way  in  which  this  species  obtained 
a  foothold  in  Madeira  and  supplanted  another  introduced  species, 
Pheidole  megacephala  Fabr. 

COCCID^E   AND   APHIDIDiE. 

The  liquid  excretions  of  the  various  species  of  scale  insects  and 
aphides  form  one  of  the  chief  sources  of  food  for  the  Argentine  ant. 
The  large  variety  of  trees  and  plants  in  the  South  gives  support  to  a 
great  number  of  coccids  and  plant  lice,  and  these  insects  in  turn 
yield  sustenance  to  myriads  of  ants.  In  return  for  this  food  supply 
the  ants  shelter  and  protect  these  insects,  with  the  result  that  the 
latter  increase  beyond  all  customary  proportions.  As  the  result  of 
this  symbiotic  manner  of  living  we  find  that  a  comparatively  small 
area  of  land  frequently  supports  enormous  numbers  of  ants,  scale 
insects,  and  aphides,  while  the  plants  themselves  become  so  severely 
infested  that  some  of  them  are  killed  and  many  more  seriously 
injured. 

All  through  the  summer  months,  and  also  during  warm  days  in 
winter,  heavy  streams  of  ants  can  be  seen  ascending  and  descending 
the  trees  and  plants;  the  ascending  ants  empty,  the  descending  ones 
heavily  laden  with  the  liquid  excretion  which  they  have  obtained 
from  the  various  scale  insects  and  plant  lice.  During  the  summer 
this  activity  is  well-nigh  endless,  and  the  ant  trails  can  be  observed 
at  all  hours  of  the  day  and  night.  All  scales  and  aphides  are  closely 
attended,  but  some  species  appear  to  attract  more  of  the  ants  than 
do  others.  The  large  unarmored  scales  and  the  plant  lice  appear  to 
be  the  chief  favorites,  the  mealy-bugs,  however,  following  them  very 
closely  in  this  regard. 

Aside  from  protecting  the  aphides  and  scale  insects  from  ladybird 
beetles  and  constructing  earthen  shelters  over  them,  the  ants  only 
rarely  foster  them  directly.  In  one  case  only  have  insects  of  this 
character  been  actually  found  in  the  ants'  nests.  In  January,  1909, 
Mr.  G.  D.  Smith,  in  excavating  an  underground  colony  at  Baton 
Rouge,  found  a  number  of  barnacle  scales,  Ceroplastes  cirripediformis 
Comst.,  on  tree  roots  which  passed  through  the  formicary.  These 
scale  insects  were  full  grown  and  vigorous.  At  this  season  of  the 
year  no  live  scales  of  this  species  could  be  found  above  ground.  It 
may  be  remarked  in  passing  that  this  is  one  of  the  species  to  which 
the  ants  are  very  attentive  during  the  summer  and  autumn  months. 

1  Notes  on  the  Habits  of  the  Argentine  or  "New  Orleans"  Ant,  Iridomyrmex  humilis  Mayr.    Wilmon 
Newell,  Journ.  Econ.  Ent.,  vol.  1,  no.  1,  pp.  21-34, 1908. 


RELATIONS   WITH    OTHER  ARTHROPODA.  63 

Workers  are  often  seen  carrying  plant  lice  and  scale  insects,  and 
this  fact,  coupled  with,  the  observed  phenomenal  spread  of  scales  in 
ant-infested  territory,  brings  one  inevitably  to  the  conclusion  that 
the  workers  carry  and  establish  these  pests  upon  new  growth  and 
upon  new  host  plants. 

During  March,  1910,  a  considerable  number  of  adult  female  scale 
insects  were  found  embedded  in  a  band  of  "tree  sticky''  placed  around 
a  magnolia  tree  to  repel  the  ants.  This  band  was  located  4  feet  from 
the  ground.  The  scale  insects  were  a  species  of  Odonaspis  *  which 
is  found  upon  Bermuda  grass  close  to  the  surface  of  the  ground. 
There  was  apparently  no  other  way  for  these  insects  to  get  up  the 
tree  except  through  the  transporting  agencies  of  the  ants. 

On  sugar  cane  the  ants  have  frequently  been  seen  carrying  around 
small  sugar-cane  mealy-bugs.  They  do  not  appear  to  pick  them  up 
unless  they  are  rudely  disturbed  or  frightened,  but  the  fact  remains 
that  they  have  been  seen  transporting  them.  Experiments  made  by 
the  junior  author  showed  that  the  ants  would  pay  no  attention  to  the 
larval  mealy-bugs  until  after  the  latter  had  commenced  to  feed  on  the 
canes  and  produce  exudations.  The  following  three  paragraphs  are 
quoted  from  our  notes: 

Placed  a  piece  of  paper  on  which  were  about  2,000  "seed  mealy-bugs"  across  a 
strong  ant  trail,  and  weighted  it  down  flat,  so  that  the  ants  could  not  get  underneath 
it.  At  first  the  ants  were  bewildered  at  losing  their  trail,  and  ran  over  the  paper  in 
all  directions.  They  absolutely  refused  to  notice  the  young  mealy-bugs,  and  after  a 
while  reestablished  their  trail  across  the  paper,  and  commenced  traveling  the  same 
as  before.-  The  mealy-bugs  were  swarming  directly  across  the  trail,  but  the  ants  paid 
no  attention  to  them. 

This  seems  to  indicate  that  the  ants  have  no  dealings  with  the  mealy-bugs  until 
they  begin  to  secrete  the  juices  from  the  cane  stalks.  These  young  mealy-bugs  had 
never  fed,  being  taken  directly  from  the  tube  in  which  they  were  hatched.  Thus 
they  would  probably  not  have  excreted  any  liquid.  At  the  same  time  the  ants  did 
not  show  any  hostility  toward  them. 

The  eggs  are  out  of  reach  of  the  ants  when  they  are  enveloped  in  the  egg  mass,  as 
the  waxy  covering  appears  to  entangle  the  feet  of  the  ants,  being  slightly  sticky  and 
adhesive.  The  egg  stage  and  young  larval  stages  are  therefore  removed  from  the 
sphere  of  the  ants'  influence. 

Even  though  the  actual  transportation  of  plant  lice,  aphides,  and 
mealy-bugs  by  the  ants  may  not  assume  much  economic  importance, 
there  is,  nevertheless,  no  doubt  that  the  ants  assist  these  insects 
greatly  in  other  ways.  They  build  shelters  over  them,  these  consist- 
ing of  fine  particles  of  earth,  protecting  them  from  storms  and  hin- 
dering the  attacks  of  parasites.  These  shelters  have  been  noticed 
in  many  different  localities.  In  Bulletin  52,  Bureau  of  Entomology, 
Mr.  E.  S.  G.  Titus  gives  an  illustration  of  a  large  shed  built  by  the  ants 
over  the  surface  of  a  persimmon,  protecting  a  number  of  Florida  wax 
scales  (Ceroplastes  floridensis  Comst.).     These  sheds  are  also  present 

1  Determined  by  Mr.  E.  R.  Sasscer. 


64  THE   ARGENTINE   ANT. 

in  great  numbers  on  sugar  cane,  Johnson  grass,  willows,  and  oaks, 
and,  in  fact,  in  all  places  where  a  number  of  coccids  or  plant  lice  are 
exposed  to  the  weather. 

The  stimulation  resulting  from  the  attentions  of  the  ants  while 
collecting  the  sweet  liquids  appears  to  have  the  effect  of  greatly 
encouraging  the  numerical  increase  of  the  aphidids  and  coccids. 
During  the  summer  of  1910  the  junior  author  reared  several  genera- 
tions of  sugar-cane  mealy-bugs  on  sugar  cane  planted  in  large  pots. 
One-half  of  these  pots  were  isolated  from  the  Argentine  ants,  while 
to  the  others  they  were  allowed  free  access.  The  mealy-bugs  grew 
and  multiplied  hi  both  lots  of  cane,  but  there  was  great  difference 
between  the  thriftiness  of  the  isolated  and  nonisolated  msects.  In  the 
pots  to  which  the  ants  had  access  the  mealy-bugs  multiplied  so  freely 
that  finally  they  almost  smothered  out  the  sugar  cane  with  their 
cottony  egg  masses.  In  the  isolated  pots,  while  the  mealy-bugs 
increased  in  numbers,  they  were  not  nearly  so  numerous  or  healthy 
looking  as  in  the  ant-infested  pots.  At  the  end  of  two  months  the 
number  of  mealy-bugs  in  the  ant-infested  pots  probably  exceeded 
the  number  of  mealy-bugs  in  the  isolated  pots  to  the  extent  of  at 
least  five  to  one. 

That  the  same  conditions  exist  in  the  cane  fields  is  shown  by  the 
number  of  mealy-bugs  which  can  be  found  in  the  fields  infested  by 
the  Argentine  ant  as  compared  to  their  scarcity  in  fields  not  infested 
by  the  ant.  Only  one  field  under  the  latter  conditions  has  been  dis- 
covered as  yet,  but  it  has  been  watched  closely  for  two  years.  The 
mealy-bugs  have  never  become  sufficiently  numerous  to  attract  the 
attention  of  the  working  hands,  and  they  can  be  found  only  with 
considerable  difficulty.  On  the  other  hand,  hi  the  fields  where  the 
mealy-bugs  and  ants  are  associated  the  former  have  become  so 
numerous  that  the  white  cottony  egg  masses  can  be  easily  observed 
from  the  road  while  driving  through  the  fields. 

The  same  thing  holds  true  with  scale  insects  generally.  In  the 
orange  groves  invasion  by  the  ants  is  followed  by  a  rapid  increase  of 
scale  insects,  particularly  the  chaff  scale  (Parlatoria  pergandii  Corns t.) 
and  various  species  of  Lecanium.  So  rapidly  do  these  scales  increase 
that,  unless  prompt  measures  are  taken  against  the  ants,  the  second 
year  of  infestation  shows  a  severe  curtailment  of  the  crop,  and  the 
fourth  or  fifth  year  witnesses  the  death  of  many  of  the  trees.  The 
rapid  decline  of  orange  trees  under  conditions  of  heavy  ant  infestation 
is  well  illustrated  by  Plate  VI,  which  shows  a  tree  after  exposure  to 
attacks  of  the  ants  and  chaff  scales  for  three  seasons. 

The  ants  constantly  attend  the  citrus  white  fly  (Aleyrodes  citri 
K.  &  H.),  and  a  marked  increase  in  this  injurious  pest  always  accom- 
panies ant  infestation. 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  VI, 


Orange  Tree  After  Exposure  to  Argentine  Ants  for  Three  Seasons.  (Original.) 


RELATIONS    WITH    OTHER   ARTHROPODA.  65 

During  a  period  of  18  months  48  species  of  scale  insects  have  been 
collected  in  Audubon  Park,  New  Orleans,  all  of  which,  are  attended 
by  the  Argentine  ant.  Many  of  these  species,  however,  are  visited 
sparingly,  and  are  evidently  regarded  as  sources  of  food  when  the 
more  popular  species  fail  to  furnish  a  sufficient  amount  for  the  needs 
of  the  ants.  A  few  species  are  particularly  favored  by  the  ants,  and 
the  trees  and  plants  upon  which  they  occur  are  always  crowded  with 
large  numbers  of  the  workers. 

Among  these  favored  species  may  be  mentioned  the  Magnolia  scale 
(Neolecanium  cornuparwim  Thro),  which  is  found  upon  the  various 
magnolia  trees.  This  scale  is  very  large  and  unarmored,  and  the 
young  scales  appear  in  great  numbers  during  February  and  March. 
As  this  is  the  period  during  which  the  ants  have  the  greatest  difficulty 
in  securing  sufficient  food  it  naturally  follows  that  they  concentrate 
upon  the  magnolia  trees  in  immense  numbers,  and  the  soil  at  the 
bases  of  the  trees  is  turned  into  gigantic  ant  nests.  During  June  and 
July  this  scale  is  brought  under  control  by  the  larva  of  a  small  black 
ladybeetle,  and  the  number  of  ants  in  the  magnolia  trees  falls  off 
greatly.  By  this  time,  however,  an  abundance  of  scale  insects  and 
plant  lice  of  many  different  species  can  be  found  everywhere,  and  the 
ants  do  not  have  to  place  such  dependence  upon  the  magnolia  scale. 

Another  species  which  attracts  great  numbers  of  workers  is  the  soft 
scale  (Coccus  Jiesperidum  L.).  This  species  has  been  collected  upon 
a  variety  of  plants  in  Audubon  Park,  among  which  may  be  mentioned 
the  orange,  banana,  Camellia  japonica,  coral  tree,  cocoa  tree,  rubber 
trees,  myrtle,  and  maidenhair  ferns.  This  scale  can  be  found  in  all 
stages  at  almost  anytime  of  the  year,  and  is  always  heavily  attended 
by  ants. 

Other  important  scale  insects  from  the  Argentine  ant's  point  of 
view  are  the  sugar-cane  mealy-bug  (Pseudococcus  calceolaria  Mask.), 
the  two  barnacle  scales  (Ceroplastes  cirripediformis  Comst.  and 
C.Jloridensis  Comst.) ,  and  the  black  scale  (Saissetia  olese  Bern.) .  The 
last  three  species  are  found  upon  a  variety  of  plants. 

A  complete  list  of  the  scale  insects  and  aphides  which  this  ant 
attends  would  comprise  a  check  list  of  these  species  for  the  entire 
ant-infested  territory.  The  following  list,  however,  includes  the 
more  important  species  upon  various  plants  and  crops  which  are  the 
most  eagerly  sought  after  by  the  ants.  Most  of  the  determinations 
have  been  made  at  Washington,  D.  C,  through  the  courtesy  of 
Messrs.  E.  R.  Sasscer,  J.  G.  Sanders,  and  Theo.  Pergande.  So  far  as 
possible  the  species  most  attractive  to  the  ants  have  been  placed 
nearest  the  host  plants,  and  they  follow  hi  order  of  preference  within 
certain  limits. 

75508°— Bull.  122—13 5 


66  THE   ARGENTINE   ANT. 

LIST    OF   COCCID.E    AND    APHIDIDS    ATTENDED    BY   THE    ARGENTINE    ANT. 

Upon  bamboos:  Asterolecanium   bambusx   Bdv.,  Odonaspis   secreta   Ckll.,  Odonaspis 

inusitata  Green. 
Upon  banana:  Coccus  hesperidum  L.,  Chrysomphalus  aonidum  L. 
Upon  cotton:  Aphis  gossypii  Glov. 

Upon  corn:  Undetermined  aphis  (probably  Aphis  maidis  Fitch). 
Upon  figs:  Pseudococcus  citri  Risso,  Lecaniodiaspis  sp.,  Aspidiotus  camellix  Sign. 
Upon  hickory,  elm,  hackberry,  and  various  shade  trees:  Pseudococcus  sp.,  Ceroplastcs 

cirripediformis  Comst.,  Ceroplastes  fioridensis  Comst.,  Chionaspis  longiloba  Cooley, 

Chionaspis  americana  Johnson. 
Upon  magnolias:  Neolecanium  cornuparvum  Thro,  Aspidiotus  camellise  Sign.,  Toumey- 

ella  turgida  Ckll. 
Upon  mulberries:  Chrysomphalus  tenebricosus  Comst. 
Upon  oaks:  Kermes  galliformis  Riley.   Eulecanium  caryx  Fitch,   Eulecanium  quer- 

cifex  Fitch,  various  aphidids. 
Upon  orange:  Coccus  hesperidum  L.,  Parlatoria  pergandii  Comst.,  Lepidosaphes  beclcii 

Newm.,  Lepidosaphes  gloverii  Pack.,   Chrysomphalus  aonidum  L.,  Aphis  gossypii 

Glov.;  also  the  white  fly,  Aleyrodes  citri  R.  &  H. 
Upon  palms  and  other  ornamentals:  Coccus  hesperidum  L.,  Eucalymnatus  tessellatus 

Sign.,  Aspidiotus  latanix  Sign.,  Aspidiotus  hederx  Vail.,  Chrysomphalus  dictyospermi 

Morg. 
Upon  peach,  pear,  and  other  fruits:  Aspidiotus  perniciosus  Comst.,  Aulacaspis  penta- 

gona  Targ.,  various  aphidids. 
Upon  persimmons:  Ceroplastes  cirripediformis  Comst.,  Eulecanium  corni  Bouche,  Pulvi- 

naria  vitis  L. 
Upon  strawberry:  Aphis forbesi  Weed. 

Upon  sugar  cane:  Pseudococcus  calceolarix  Mask.,  Aphis  gossypii  Glov. 
Upon  sweet  gum:  Cryptophyllaspis  liquidambaris  Kotinsky. 
Upon  various  shrubs:  Coccus  hesperidum  L.,  Saissetia  olex  Bern.,  Pulvinaria  cupamx 

Ckll.,  Aspidiotus  latanix  Sign..  Chrysomphalus  aonidum  L. 
Upon  willows:  Eulecanium  nigrofasciatum  Perg.,  Pseudococcus  sp.  (near  citri),  Chion- 
aspis salicis-nigrx  Walsh,   Aspidiotus    perniciosus  Comst.,   various  undetermined 

aphidids. 

In  considering  the  remarkable  increase  in  scale  insects  and  aphidids 
which  invariably  accompanies  heavy  infestation  by  this  ant  one  can 
not  avoid  taking  into  account  the  persistence  with  which  the  ants 
drive  away  ladybird  beetles  which  attempt  to  prey  upon  the  insects 
fostered  by  the  ants.  So  thoroughly  are  the  Coccidas  and  Aphididae 
protected  in  this  manner  that  it  is  rare  that  a  ladybird  can  be  found 
at  all  on  the  infested  trees.  The  only  exceptions  to  this  rule  thus 
far  noted  are  a  species  of  Pentilia,  a  few  specimens  of  which  the 
senior  author  found  in  an  infested  orange  grove  below  New  Orleans, 
and  the  coccinellid  mentioned  before  as  preying  upon  the  magnolia 
scale. 

ANTAGONISM    TOWARD    OTHER    INSECTS. 

The  Argentine  ant  is  strongly  antagonistic  to  nearly  all  forms  of 
insect  life,  with  the  exception  of  the  Coccidae  and  Aphididas.  The 
amount  of  damage  it  is  able  to  inflict  upon  other  insects,  however,  is 
governed   by   the   strength,   fleetness,   structure,    or  habits   of   the 


RELATIONS   WITH    OTHER   ARTHROPODA.  67 

insect  attacked.  Thus  it  is  able  to  destroy  house  flies,  butterflies, 
mosquitoes,  etc.,  only  when  the  latter  are  hurt  or  disabled,  as 
under  ordinary  conditions  they  are  much  too  swift  for  the  ants  to 
catch.  In  the  same  manner  nearly  all  forms  of  beetles  are  strong 
enough  to  escape  from  the  ants  when  caught,,  and  their  external 
covering  is  so  hard  that  the  ants  can  make  no  impression  upon  it; 
but  an  injured  beetle  of  any  kind  is  very  quickly  overcome  by  the 
numbers  of  the  ants,  and  his  body  is  finally  cleaned  out  of  the  shell 
piecemeal.  Newly  emerged  adult  beetles  of  many  species  are  often 
captured  by  the  ants  before  their  chitinous  integument  has  hardened, 
and  they  are  then  an  easy  prey. 

Cutworms  and  hairless  caterpillars  found  upon  the  surface  of  the 
ground  are  destroyed  in  great  numbers;  but  the  ants  will  not  burrow 
into  the  ground  after  hidden  cutworms,  and  most  hairy  caterpillars 
appear  to  be  invulnerable  to  them.  Web-spinning  caterpillars  are 
also  safe  from  their  attacks,  and  the  spiny,  mealy  projections  sur- 
rounding coccinellid  or  ladybeetle  larvae  appear  to  protect  these 
latter  very  effectively.  Insects  and  other  small  related  animals  which 
the  ants  can  meet  upon  even  terms  are,  however,  almost  always  over- 
come; not  so  much  on  account  of  the  individual  valor  of  the  Argen- 
tine ants  as  by  reason  of  their  overpowering  numbers. 

Nests  of  the  social  wasps,  Polistes  sp.,  which  were  brought  into  our 
laboratory  as  food  supplies  for  cultures  of  Pediculoides,  were  quickly 
found  by  foraging  workers,  and  the  latter  soon  killed  and  removed 
all  of  the  wasp  larvae  and  pupae  that  could  be  reached.  Many  of  the 
cells  in  the  comb  of  Polistes  were  entirely  or  partially  open  so  that 
the  ants  had  ready  access  to  the  insects  inside.  As  the  prey  in  this 
case  was  too  large  to  be  handled  by  individual  ants,  as  many  as  two 
or  three  dozen  would  unite  in  removing  a  single  wasp  pupa  or  larva. 
Even  the  adult  wasps,  just  emerging  from  the  cells,  were  set  upon  by 
the  ants  before  they  had  attained  sufficient  strength  to  escape  by 
flight.  More  and  more  of  the  ants  would  get  on  these  adult  wasps 
until  the  latter  were  helpless  and  were  dragged  away,  still  alive,  by 
scores  of  the  worker  ants.  So  anxious  were  the  ants  to  get  at  these 
wasps  that  when  the  latter  were  placed  on  top  of  a  fruit  jar  standing 
in  a  tray  of  water  the  ants  swam  the  3  inches  of  fresh  water,  climbed 
the  glass  sides  of  the  jar,  and  continued  their  attacks  as  before;  nor 
could  they  be  made  to  desist  until  oil  of  sassafras  was  placed  upon 
the  water. 

The  nests  of  mud-dauber  wasps,  Pelopoeus  sp.,  were  also  brought 
into  the  laboratory  for  the  same  use  as  the  Polistes.  The  mud- 
dauber  larvae  were  of  course  inaccessible  to  the  ants,  but  parasitic 
flies  1  which  emerged  from  these  were  seized  by  the  ants  as  fast  as 

1  Identified  by  Mr.  C.  H.  Tyler  Townsend  as  a  species  of  Pachyophthalmus. 


68  THE   ARGENTINE  ANT. 

they  emerged  and  were  summarily  disposed  of  in  the  same  manner 
as  were  the  Polistes.  Invariably  the  flies  were  seized  before  enough 
time  had  elapsed  for  their  wings  to  expand  and  dry,  and  only  a  very 
small  percentage  of  them  escaped  the  ants. 

Cockroaches  are  esteemed  a  great  delicacy  by  these  ants,  and  while 
the  workers  are  not  able  to  capture  uninjured  roaches,  they  attack 
in  great  numbers  any  roach  so  unlucky  as  to  be  injured.  Dead  cock- 
roaches are  also  eagerly  visited  by  the  ants  and  all  soft  parts  removed. 
It  seems  almost  retribution  that  one  of  the  few  natural  enemies  of  the 
Argentine  ant  should  itself  be  a  larval  cockroach  (Thyrsocera  cincta 
Burm.),  mention  of  which  is  made  on  a  following  page. 

THE  ARGEXTIXE  AXT  AXD  THE  BOLL  WEEVIL. 

Prior  to  the  advent  of  the  boll  weevil  in  the  territory  infested  by  the 
Argentine  ant  there  was  considerable  speculation  as  to  whether  so 
combative  an  ant  might  not  prove  to  be  an  insect  of  some  value  in 
protecting  the  cotton  crop  against  weevil  ravages.  Any  hopes  of  this 
kind  which  were  entertained  have  not  thus  far  been  realized.  In  one 
rather  unimportant  respect  the  ants  seem  to  annoy  the  boll  weevils. 
At  Baton  Rouge  the  Louisiana  Experiment  Station  had  a  few  small  plats 
of  cotton,  aggregating  less  than  an  acre,  within  the  city  limits  and  in  a 
section  where  the  Argentine  ants  were  exceedingly  abundant.  The 
plats  were  bordered  on  one  side  by  the  Louisiana  State  LTniversity 
campus,  with  its  large  oak  trees  sheltering  hundreds  of  ant  colonies, 
and  on  the  other  side  by  the  batture  of  the  Mississippi  River,  which 
was  likewise  a  seething  mass  of  ant  colonies.  The  ground  in  the  cotton 
plats  was  therefore  heavily  infested  by  the  ants,  and  when  this  field 
also  became  infested  by  the  boll  weevil  the  outcome  was  watched  with 
considerable  interest.  During  September,  1909,  it  was  found  that 
the  ants,  in  their  steady  patrol  of  the  plants  while  attending  cotton 
lice,  worried  the  adult  boll  weevils  considerably.  Whenever  an  ant 
encountered  a  boll  weevil  it  would  nip  the  legs  of  the  latter,  usually 
causing  the  weevil  to  fly  to  another  plant  or  drop  to  the  ground.  In 
no  case  were  the  ants  found  killing  fully  matured  weevils,  though  in  a 
few  instances  they  did  attack  and  kill  unhardened  weevils  which  had 
just  issued  from  infested  squares.  The  great  abundance  of  ants  in 
these  plats  evidently  resulted  in  many  of  the  weevils  being  driven  ofT, 
for  something  of  a  top  crop  was  produced  in  the  fall  of  1909.  It  is 
worthy  of  note  in  this  connection  that  the  heavy  ant  infestation 
obtaining  in  these  plats  will  not  be  duplicated  in  large  cotton  fields 
for  many  years  to  come,  if,  indeed,  such  wTill  ever  be  the  case.  Condi- 
tions in  large  cotton  areas  are  not  such  as  to  attract  the  Argentine  ant 
in  numbers.  It  was  also  of  interest  to  note  that  the  presence  of  the 
ants  in  these  particular  plats  resulted  in  an  abnormally  heavy  infesta- 


RELATIONS    WITH    OTHER   ARTHROPODA.  69 

tion  of  the  plants  by  the  "cotton  louse,"  Aphis  gossypii  Glov., 
throughout  the  entire  growing  season. 

Were  the  jaws  of  the  Argentine  ant  powerful  enough  to  pierce  the 
cotton  squares  so  that  they  could  remove  the  boll-weevil  larvae,  and 
were  they  so  inclined,  they  might  be  of  substantial  service  in  destroy- 
ing this  pest.  However,  repeated  experiments  made  by  the  senior 
author  proved  conclusively  that  the  ants  would  not  do  this.  The 
following  experiment  will  serve  as  an  illustration  of  those  carried  out: 

On  July  10,  1908,  three  weevil-infested  squares  were  placed  en  the 
food  table  of  an  Argentine-ant  colony  in  the  insectary  at  Baton  Rouge. 
The  workers  crawled  over  them  constantly  for  three  hours,  but  made 
no  attempt  to  bite  into  them  and  evidently  did  not  suspect  the  pres- 
ence of  food  inside  of  them.  Afterwards  the  weevil  larvae  were  re- 
moved from  the  squares  and  placed,  alive  and  uninjured,  on  the  food 
table.  The  ants  attacked  them,  hesitatingly  at  first  and  then  with 
avidity,  and  in  the  course  of  a  minute  one  large  weevil  larva  was 
dragged  an  inch  across  the  food  table,  vertically  another  inch,  and 
into  the  vestibule  of  the  nest.  Another  lot  of  weevil-infested  squares 
was  placed  on  a  board  inside  the  insectary  where  the  ants  had  been 
securing  other  food  for  several  days.  The  squares  were  left  here  for 
five  hours,  during  which  time  the  ants  crawled  over  them  constantly, 
but  made  no  effort  to  open  them.  The  ends  of  the  squares  were  then 
broken  off  so  that  the  ants  could  enter  them  if  they  chose.  Xone 
entered.  Presently  some  of  the  weevil  larvae  wriggled  themselves 
completely  out  of  the  squares  and  they  were  then  attacked  by  the  ants 
and  dragged  away. 

These  and  similar  experiments  lead  one  to  the  conclusion  that  the 
Argentine  ant  will  never  be  of  material  value  as  an  enemy  of  the  boll 
weevil.  In  fact,  in  this  respect  it  can  not  hope  to  approach  in  effi- 
ciency the  common  native  fire  ant,  Solenopsis  geminata  Fab. 

BENEFICIAL   ASPECTS    OP   THE    ANT's    ACTIVITIES. 

In  some  few  cases  the  predatory  habits  of  the  ant  take  on  a  bene- 
ficial aspect.  In  the  summer  of  1908  Mr.  R.  C.  Treherne  was  associ- 
ated with  us  hi  the  investigation  of  the  sorghum  midge  (Diplosis) 
Contarinia  sorgMcola  Coq.  In  the  course  of  his  work  Mr.  Treherne 
placed  heads  of  sorghum,  milo  maize,  etc.,  in  cages  for  the  purpose  of 
rearing  the  adult  midges.  In  a  very  short  time  he  found  that  the 
Argentine  ants  were  invading  the  cages  and  were  carrying  away  the 
adult  midges  almost  as  fast  as  they  emerged.  (See  fig.  10,  from  draw- 
ing by  Mr.  Treherne.)  To  continue  the  observations  it  was  necessary 
to  isolate  the  cages  over  trays  of  water  or  oil.  For  the  purpose  of 
more  closely  observing  the  capture  of  the  midges  by  the  ants,  about 
200  of  the  former  were  placed  inside  a  large  glass  bell  jar.  The  jar  was 
raised  a  trifle  at  its  lower  edge  by  the  insertion  of  a  match.     In  the 


0 


THE    ARGENTINE    AXT. 


course  of  three  minutes  two  Argentine  workers  had  found  their  way 
into  the  jar  and  each  had  captured  an  adult  midge.  Other  workers 
soon  followed.  In  about  15  minutes  fully  three-fourths  of  the  flies 
had  been  captured  and  at  the  end  of  30  minutes  all  had  been  either 
captured  and  carried  away  or  were  in  possession  of  workers.  The 
first  midges  captured  were  quickly  carried  to  the  ants'  nest,  but  pres- 
ently the  workers  seemed  less  appreciative  of  their  prizes  and  spent 
much  more  time  in  playing  with  them,  although  in  but  few  cases  were 
the  midges  relinquished.  Occasionally  a  midge  would  succeed  in 
taking  flight  after  a  worker  had  taken  hold  of  it;  in  such  cases  worker 
and  midge  tumbled  to  the  floor,  but  without  the  midge  being  released. 
That  the  workers  were  unable  to  see  the  midges  was  made  evident 

many  times  over  hi  this  experi- 
ment, for  workers  repeatedly  passed 
within  one-sixteenth  of  an  inch  of 
their  prey  without  even  changing 
the  direction  of  travel.  Only  when 
the  worker  touched  the  midge  with 
her  antenna?  could  she  locate  the 
latter. 

Later  on  it  was  found  that  the 
ants  thoroughly  patrolled  the  sor- 
ghum heads  in  the  field  and  not  only 
captured  the  nudges  as  they  were 
emerging  from  their  pupal  cases  be- 
tween the  glumes  but  also  removed 
the  pupa?  themselves.  That  this 
ant  is  by  far  the  most  important 
natural  enemy  of  the  sorghum  midge 
in  southern  Louisiana  there  can  be 

Fig.  10.-Argentine  ant  removing  the  pupa  of  a      HO    doubt,1   but    its   Services   ill    this 
sorghum  midge  from  between  the  glumes  of  a     regard  do    not   begUl   to    expiate   its 

sorghum  head.    (Original.)  . 

many  other  crmies. 
The  Argentine  ant  is  a  persistent  enemy  of  the  white  ants,  or 
termites,  and  will  capture  and  kill  them  at  every  opportunity.  Espe- 
cially during  the  mating  season  of  the  termites  even'  male  and  queen 
that  falls  to  earth  is  quickly  set  upon  by  the  ants.  The  latter  cut 
off  their  wings,  and  frequently  also  legs  and  antenna?,  and  then  bear 
them  away,  still  alive,  to  their  nests.  Wherever  colonies  of  termites 
are  accidentally  exposed  the  ants  soon  destroy  them,  carrying  away 
all  stages.  Xot  iiifrequently  one  finds  the  Argentine  ant  colonies 
domiciled  in  the  old  termite  galleries  in  logs  and  timbers,  the  assump- 
tion being  that  the  ants  had  first  destroyed  the  termite  colonies  and 
then  taken  possession  of  their  domiciles.     When  winged  termites  were 


Dean,  Harper,  Bui.  85,  Part  IV,  rev.,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  p.  57, 1911. 


Relations  with  otheh  arthropoda.  71 

furnished  to  the  ants  in  our  artificial  formicaries  the  wings  were 
quickly  amputated,  although  the  termite  itself  was  not  always  carried 
into  the  formicary,  possibly  because,  in  such  cases,  the  ants  were 
already  bountifully  supplied  with  animal  food. 

The  Rev.  Albert  Biever,  of  New  Orleans,  whose  observations  on 
the  Argentine  ant  are  elsewhere  mentioned,  is  authority  for  the 
statement  that  these  ants  have  in  many  cases  entirely  exterminated 
the  bedbugs  in  the  houses  of  many  of  the  poorer  people  in  New 
Orleans. 

Father  Biever  also  states  that  in  some  sections  of  the  city  the 
"red  bug,"  or  chigger,  has  entirely  disappeared  with  the  advent  of 
the  ants.  The  junior  author's  observations  in  Audubon  Park,  New 
Orleans,  are  of  similar  nature,  the  chiggers  being  entirely  absent 
where  once  they  were  a  plague.  At  the  same  time  the  senior  author 
•still  retains  some  very  unpleasant  memories  of  daily  attacks  by 
chiggers  on  premises  in  Baton  Rouge  which  were  heavily  infested 
by  the  ants.  We  are  thus  unable,  as  yet,  to  state  with  certainty 
that  the  ants  always  destroy  these  annoying  pests. 

The  attitude  of  the  Argentine  ant  toward  other  species  of  ants  has 
already  been  discussed  and  its  action  in  destroying  other  ants  takes 
on  either  a  beneficial  or  injurious  aspect  according  to  whether  the 
annihilated  ant  is  itself  one  of  beneficial  or  injurious  nature. 

symbiotic  relations. 

The  relationships  which  exist  between  the  Argentine  ant  and  those 
insects  or  other  creatures  which  it  tolerates  in  its  nests  or  in  the 
near  vicinity  can  not  be  considered  as  symbiosis,  yet  mention  of  these 
may  be  permissible  at  this  point.  Despite  the  hostility  which  these 
ants  exhibit  toward  most  insects  which  are  not  directly  of  service 
to  them,  a  few  instances  have  been  noted  in  which  other  insects  and 
crustaceans  were  permitted  to  live  in  close  proximity  to  their  nests, 
or  even  within  the  nests  themselves. 

Certain  staphylinid  beetles  have  frequently  been  found  in  decayed 
logs  which  were  full  of  Argentine  ants.  Efforts  have  been  made  to 
keep  some  of  these  beetles  in  the  artificial  formicaries  along  with 
colonies  of  the  ant  under  observation,  but  the  results  have  been 
variable.  In  experiments  of  this  kind  made  by  the  junior  author 
the  beetles  were  invariably  set  upon  by  the  ants  in  the  formicary 
and  either  killed  or  driven  out.  In  similar  experiments  by  the 
senior  author  no  apparent  attention  was  paid  to  the  beetles,  so  far 
as  could  be  observed,  and  they  were  tolerated  in  the  formicary  for  a 
week  or  longer,  after  which  they  evidently  left  of  their  own  accord. 

On  August  17,  1909,  a  large  ant  nest  was  discovered  in  Baton 
Rouge  under  a  large  dry-goods  box.     About  20  specimens  of  "spittle 


i  2  THE   ARGENTINE   ANT. 

insects"  (family  Cercopidae)  were  also  present  in  the  same  nest, 
attached  to  straws  of  grass.  These  were  apparently  protected  from 
the  ants  by  the  wet,  sticky  secretion  which  surrounded  them.  This 
is  the  only  instance,  however,  in  which  the  presence  of  these  insects 
has  been  recorded  in  the  colonies. 

Sowbugs  (Oniscida?)  apparently  go  among  the  Argentine  ants  with 
impunity.  These  little  crustaceans  are  often  found  in  the  ant 
nest,  especially  if  they  are  located  under  boards  or  boxes  in  moist 
places.  There  does  not  appear  to  be  any  relationship  existing,  and 
the  ants  are  apparently  indifferent  to  their  presence. 

With  the  exception  of  two  species  of  mites,  which  are  true  inquilines 
in  the  ant  colonies,  the  Argentine  ant  does  not  pay  much  attention 
to  the  majority  of  mites  and  spiders.  Mention  is  made  on  a  later 
page  of  certain  spiders  which  prey  upon  the  ants  to  a  limited  extent. 
The  cattle  tick  (Margaropus  annulatus  Say)  flourishes  with  undi- 
minished vigor  in  the  ant-infested  region,  and  the  same  may  be  said 
of  the  "red  mite"  of  the  orange  and  the  red  spider  of  ornamental 
plants  (Tetranychus  bimaculatus  Harv.). 

INQUILINES. 

Only  two  true  inquilines,  both  mites,  have  thus  far  been  found  in 
the  colonies  of  the  Argentine  ant.  These  were  first  discovered  at 
Baton  Rouge  by  the  senior  author  in  1908,  and  were  subsequently 
found  in  various  localities  and  in  nests  of  various  kinds,  usually  in 
those  located  in  masses  of  decaying  vegetation  or  littero  Soon  after 
they  were  first  found  specimens  were  sent  to  Dr.  L.  O.  Howard,  who 
submitted  them  to  Mr.  Nathan  Banks,  of  the  Bureau  of  Entomology. 
Mr.  Banks  found  them  to  be  new,  and  his  descriptions  of  them  were 
published  in  the  Journal  of  Economic  Entomology,  volume  1,  pages 
263  and  264  (1908),  together  with  notes  on  their  habits,  by  the  senior 
author. 

NATURAL  CONTROL. 

As  compared  with  most  injurious  insects  which  reach  great  abun- 
dance the  Argentine  ant  is  remarkably  free  from  natural  enemies, 
and  very  few  of  these  have  been  noted  during  the  course  of  our  inves- 
tigations, while  even  these  few  are  of  little  importance.  No  true 
parasites  of  this  ant  have  been  observed,  and  apparently  the  only 
enemies  are  predatory  ones. 

NATURAL   ENEMIES. 

INSECTS   AND   SPIDERS. 

In  1909  Mr.  Harper  Dean  observed  a  small  cockroach  capturing 
Argentine  ant  workers  in  a  room  in  Baton  Rouge,  La.  This  insect 
from  time  to  time  caught  up  and  ate  workers  which  were  traveling 


NATURAL   CONTROL.  73 

about  the  floor.  The  cockroach  was  captured  and  sent  to  the  Bureau 
of  Entomology,  where  it  was  identified  by  Mr.  A.  N.  Caudell  as  a 
nymph  of  Thyrsocera  cincta  Burm.,  a  species  occurring  in  the  south- 
ern United  States,  Mexico,  and  Central  America.  A  similar  habit  by 
individuals  of  this  species  was  subsequently  observed  by  the  senior 
author  on  one  or  two  occasions,  but  the  number  of  ants  destroyed 
by  this  insect  is  certainly  inappreciable. 

A  jumping  spider  of  the  family  Attidae  was  seen  to  capture  a  few 
workers,  and  various  species  of  the  cobweb  weavers  (Theridiidae)  had 
the  habit  of  reposing  beneath  the  stands  supporting  our  artificial 
formicaries  and  there  depleting  the  colonies  under  observation.  In 
fact,  -so  persistent  were  they  that  it  was  necessary  to  examine  the 
stands  daily  and  destroy  these  spiders.  Among  the  most  abundant  of 
these  was  one  which  was  identified  by  the  late  Prof.  B.  H.  Guilbeau,  of 
the  Louisiana  State  University,  as  Theridium  tepidariorum.  Spiders 
of  this  family  were  not  observed  destroying  ants  in  outdoor  colonies, 
but  it  is  possible  that  they  do  so. 

BIRDS. 

On  one  occasion  Mr.  G.  A.  Runner  observed  an  English  sparrow 
industriously  picking  up  the  Argentine  workers  from  a  trail  which 
crossed  a  wide  roadway  at  Baton  Rouge.  This  habit  is  not,  how- 
ever, a  common  one  with  this  bird. 

The  flicker  or  yellowhammer,  Colaptes  auratus,  has  often  been  seen 
industriously  digging  up  shallow  ant  nests  in  lawns  and  grass  plats, 
evidently  for  the  purpose  of  obtaining  the  pupae  and  larvae,  and 
should  doubtless  be  credited  with  being  the  most  important  natural 
enemy  which  this  ant  has  in  the  South.  Our  knowledge  of  the  extent 
to  which  native  birds  subsist  upon  these  ants  is  very  limited  as  yet, 
and  the  subject  is  one  well  worth  more  complete  investigation  than 
we  have  been  able  to  give  it. 

EXPERIMENTS    WITH    PEDICULOIDES. 

The  idea  of  finding  some  parasite  which  would  destroy  the  ants 
naturally  suggested  itself  early  in  our  investigations.  Owing  to  the 
readiness  with  which  the  small  parasitic  mite,  Pediculoides  ventricosus 
Newp.,  parasitizes  the  larvae  of  wasps  and  beetles  whenever  it  can 
obtain  access  to  them  it  was  thought  worth  while  to  see  if  this  para- 
site could  be  successfully  used  against  the  ant.  For  our  experiments 
we  first  reared  enormous  colonies  of  these  mites  on  living  wasp  larvae 
and  thereafter  placed  these  infested  larvae  in  the  formicaries,  where 
they  could  be  closely  observed.  The  following  experiment  will  illus- 
trate the  results  obtained: 

For  the  experiment  we  selected  a  large  populous  ant  colony  which 
was  domiciled  in  a  plaster  of  Paris  Janet  cage  of  several  chambers. 


74  THE   ARGENTINE   ANT. 

All  immature  stages  of  the  ant  were  present  in  abundance.  On  March 
14  the  cover  to  one  of  the  living  chambers  was  raised  and  one  of  the 
mite-infested  larvae  was  dropped  in  among  the  workers  and  larvae  in 
the  formicary.  The  workers  set  to  work  immediately  to  kill  the 
hundreds  of  mites.  The  larval  mites  were  picked  up  in  the  workers' 
mandibles,  chewed  a  bit  and  then  thrown  aside.  Adult  mites  were 
seized  by  the  legs  and  vigorously  pulled  until  they  released  their  hold 
on  the  wasp  larvae,  after  which  the  workers  would  crush  them  in  their 
mandibles.  However,  the  subsequent  developments  were  entirely 
unexpected.  A  worker  was  seen  to  mount  the  wasp  larva,  eagerly 
destroying  mites  and  becoming  at  the  same  time  covered  with  a  dozen 
or  more  of  the  mite  larvae.  Within  a  minute  the  worker  desisted 
from  destruction  of  the  mites  about  her  and  turned  her  attention  to 
the  ones  on  her  body,  trying  to  dislodge  them  by  rubbing  head  and 
abdomen  with  her  legs.  Failing  thus  to  get  rid  of  them,  she  resorted 
to  various  gymnastic  performances,  such  as  jumping  and  rolling  over. 
Soon  afterwards  her  movements  became  slow  and  feeble  and  finally 
ceased  entirely,  it  being  evident  that  she  had  either  been  killed  or 
paralyzed  by  the  bites  of  the  larval  mites.  Observations  were  sus- 
pended until  March  18,  when  it  was  found  that  the  adults  and  larvae 
of  Pediculoides  were  greatly  reduced  in  numbers.  No  mites  could  be 
seen  on  any  of  the  ant  larvae  or  pupae,  and  all  of  the  latter  had  been 
removed  from  the  chamber  where  the  mites  were  introduced. 

The  workers  in  leaving  the  cage  to  forage  were  compelled  to  pass 
through  the  infested  chamber,  but  in  doing  so  they  made  the  widest 
possible  detour  about  the  mite-infested  material.  This  status  of 
affairs  continued  for  some  time,  the  mites  gradually  decreasing  in 
numbers  until  by  April  28  they  had  all  disappeared.  On  this  date 
cultures  of  the  mite  were  again  introduced  into  the  colony,  but  in 
much  greater  quantities  than  before.  A  spoonful  of  mite-infested 
wasp  larvae  was  placed  in  each  chamber  of  the  formicary.  The  ants 
did  not  this  time  attempt  to  kill  the  mites,  but  inside  of  two  minutes 
after  the  introduction  of  the  latter  the  colony  had  completely  deserted 
the  formicary,  taking  with  it  all  eggs,  larvae,  and  pupae.  Not  being 
able  to  find  other  suitable  quarters  on  account  of  the  water  surround- 
ing the  formicary,  the  ants  on  the  following  day  decided  to  return  to 
the  nest.  They  attempted  to  remove  the  Pediculoides,  but  the  mor- 
tality among  the  workers  was  heavy,  many  being  carried  out  at  the 
entrance.  On  the  following  day  the  number  of  dead  workers  was  too 
great  for  removal,  and  many  of  them  remained  in  the  cage.  The  con- 
tinual warfare  against  the  mites  continued  for  several  days,  the  ant 
colony  becoming  by  May  6  severely  depleted  in  workers  as  well  as 
in  larvae,  some  of  which  were  killed  by  the  mites.  At  the  same  time 
it  was  evident  that  the  Pediculoides  were  being  destroyed  much  more 
rapidly  than  they  could  increase.     After  May  6  the  ant  colony  ap- 


NATURAL   CONTROL.  75 

peared  to  recover  slowly.  By  July  22  the  colony  had  completely 
resumed  its  normal  condition  and  the  mites  had  been  exterminated. 
That  the  Pediculoides  could  live  and  breed  upon  the  ant  larvae  was 
established  by  placing  the  latter  in  a  glass  dish  which  was  isolated 
from  all  workers  and  permitting  them  to  become  infested.  On  them 
the  Pediculoides  grew  and  increased  as  well,  apparently,  as  on  wasp 
and  other  larvae.  Such  enormous  cultures  of  the  mite  as  were  intro- 
duced into  the  ant  colonies  in  these  experiments  could  not  possibly 
occur  in  nature,  and  it  seems  a  safe  conclusion  that  this  parasite  can 
make  no  headway  against  the  ant  under  normal  conditions. 

EXPERIMENTS    WITH   FUNGOUS   DISEASES. 

During  1909,  at  Baton  Rouge,  several  experiments  were  made  in 
the  attempt  to  inoculate  the  ants  and  their  larvae  with  the  chinch-bug 
fungus,  Sporotrichum  globuliferum .  Cultures  were  prepared  from 
beef  extract  and  corn  meal,  sterilized  at  a  pressure  of  18  pounds  per 
square  inch  for  30  minutes  at  a  temperature  of  256°  F.,  and  these 
were  then  inoculated  with  the  fungus  from  a  dead  beetle.  After  these 
cultures  had  been  stored  for  about  a  week  in  a  dark,  damp  place, 
they  all  showed  a  heavy  white  layer  of  fungous  growth  over  the  sur- 
face, and  this  layer  was  used  in  the  experiments. 

Large  quantities  of  this  fungus  were  placed  in  Janet  cages  which 
contained  strong  and  healthy  colonies  of  ants  with  many  immature 
stages.  For  a  short  time  the  workers  would  busy  themselves  carry- 
ing out  the  fungus  and  dropping  it  over  the  side  of  the  cage  support, 
but  after  a  time  they  apparently  became  accustomed  to  its  presence. 
It  grew  and  increased  inside  the  apartments  in  which  the  ants  and  their 
young  stages  were  domiciled  until  it  formed  a  heavy  white  mass  over 
nearly  everything,  but  in  not  a  single  instance  was  an  ant  or  a  young 
stage  observed  which  appeared  to  be  in  the  least  inconvenienced  by  it. 

As  a  number  of  dead  ants  were  found  covered  with  fungi  the 
various  organisms  on  them  were  isolated  and  cultures  made.  The 
principal  fungi  obtained  were  Aspergillus  and  Penicillium.  Cul- 
tures of  these  were  also  introduced  into  the  ant  colonies,  but  without 
effect.  It  was  therefore  concluded  that  they  were  purely  sapro- 
phytic on  the  dead  ants  on  which  they  were  found. 

Attempts  were  also  made  to  infect  colonies  with  Bacillus  larvae, 
the  germ  causing  the  disease  among  honey  bees  known  as  American 
foul  brood.  Owing  to  the  fact  that  this  bacillus  attacks  the  larval 
stages  of  the  honey  bee,  and  considering  the  similarity  of  ant  and  bee 
larvae,  it  was  thought  that  this  disease  might  attack  the  larval  stages 
of  the  ant.  The  experiments  were  made  in  a  locality  where  the  ant 
infestation  was  very  heavy  but  where  honey  bees  were  not  kept. 
Honey  was  thoroughly  mixed  with  broken  and  mashed  brood  combs 
containing  bee  larvae  badly  infected  with  foul  brood,  and  this  honey 


76  THE   ARGENTINE   ANT. 

was  then  fed  in  abundance  to  foraging  workers.  Subsequent  exami- 
nation of  the  colonies  receiving  this  infected  material  failed  to  show 
any  indication  of  the  disease. 

No  attempt  was  made  to  experiment  with  this  disease  under  labora- 
tory conditions,  on  account  of  the  danger  of  accidentally  infecting 
honey  bees  in  the  neighborhood. 

LOW    TEMPERATURES. 

The  winter  temperatures  experienced  at  Baton  Rouge,  La.,  seemed 
not  to  produce  any  appreciable  mortality  among  the  ants.  During 
the  winter  of  1909-10  a  colony  at  Baton  Rouge  was  kept  out  of  doors 
all  winter  with  no  other  protection  than  the  plaster  of  Paris  walls  of 
the  cage  in  which  it  was  confined.  This  colony  successfully  with- 
stood a  temperature  of  22°  F.,  the  lowest  temperature  recorded 
during  the  winter.  It  is  safe  to  assume  that  in  their  underground 
nests  and  in  well-protected  situations  they  can  withstand  a  much 
lower  degree  of  cold  than  this. 

FLOODS. 

Heavy  rains  appear  to  be  the  only  meteorological  phenomena 
wilich  produce  any  appreciable  effect  upon  the  Argentine  ants,  but 
even  in  this  connection  it  is  worthy  of  note  that  the  most  heavily 
infested  sections  at  present  are  within  regions  of  exceedingly  heavy 
annual  rainfall. 

After  sudden  severe  rainstorms  it  was  noticed  that  the  ditches  and 
drains  at  Baton  Rouge  and  New  Orleans  contained  thousands  of  the 
dead  ants,  evidently  washed  from  trees  and  ground  before  they  could 
reach  a  place  of  safety.  The  sudden  rising  of  flood  waters  over  low- 
lands would  appear  to  destroy  many  colonies  and  the  larvae  in  them, 
yet,  strange  to  say,  the  batture  along  the  Mississippi  River,  which  is 
annually  covered  for  several  wreeks  with  several  feet  of  water,  con- 
tinues to  be  an  area  of  approximately  maximum  infestation.  So 
facile  are  the  ants  in  migrating  to  higher  grounds  or  in  ascending 
trees,  taking  with  them  all  larvae  and  pupae,  that  it  is  likely  that  the 
mortality  from  this  source  is  much  less  than  would  be  expected. 
The  mere  destruction  of  foraging  workers  by  rains  does  not  effect  any 
appreciable  diminution  in  the  rate  of  increase  since,  if  the  colonies 
themselves  remain  unharmed,  the  deposition  of  eggs  and  the  rearing 
of  more  workers  continues  unabated. 

METHODS  OF  REPRESSION. 

It  is  as  a  household  pest  that  the  Argentine  ant  has  forced  itself 
most  into  prominence,  particularly  in  the  infested  cities  and  towns, 
although  it  is  doubtful  if  the  financial  loss  due  to  its  inroads  in  this 


METHODS   OF    REPRESSION.  77 

respect  even  begins  to  compare  "with  the  losses  suffered  by  the  florists, 
bee  keepers,  and  orange  growers.  Early  in  the  course  of  our  studies 
we  undertook  experiments  looking  to  the  development  of  measures 
by  which  householders  could  obtain  some  relief  from  this  pest. 

A  successful  campaign  against  the  Argentine  ant  is  by  no  means 
devoid  of  work,  but  the  control  measures  thus  far  devised  are  no 
more  cumbersome  or  expensive  than  those  employed  in  the  warfare 
against  many  other  insects,  and  their  intelligent  employment  is  found 
well  worth  the  while  in  reduced  annoyance  from  this  pest. 

Studies  of  the  ant's  life  history  early  developed  the  fact  that  per- 
manent relief  can  be  obtained  only  by  actual  destruction  of  the  ants 
themselves.  The  use  of  repellents  only  serves  to  permit  the  contin- 
ued increase  of  the  pests  and  to  postpone  the  time  when  more  laborious 
methods  of  warfare  must  be  adopted.  Not  only  is  it  necessary  to 
kill  the  ants  outright,  but  it  is  also  necessary  to  adopt  means  which 
will  kill  the  queens.  It  is  hardly  necessary  to  call  attention  to  the 
difference  between  killing  ants  and  the  usual  insects  with  which  we 
have  to  contend.  If  one  kills  a  female  gipsy  moth  or  boll  weevil,  for 
example,  possible  future  progeny  of  that  particular  individual  is  made 
impossible.  Such  is  not  the  case  when  one  destroys  a  worker  ant, 
for  the  rate  of  increase  and  the  development  of  future  generations  are 
in  no  way  interfered  with.  This  is  true  for  the  reason  that  the  workers 
take  no  part  in  reproduction,  all  eggs  being  deposited  by  the  queens. 
That  the  destruction  of  foraging  workers  does  not  materially  affect 
the  domestic  economy  of  the  colony  or  retard  the  rate  of  increase  by 
reducing  the  available  food  supply  is  shown  by  repeated  observations 
upon  the  number  of  foragers  required  to  keep  the  colony  supplied  with 
food.  In  the  artificial  formicaries  counts  were  made  of  the  number 
of  workers  going  out  for  food  during  periods  varying  from  five  hours 
to  several  days,  and  in  no  case  did  the  number  of  foraging  workers 
out  at  one  time  exceed  more  than  1  per  cent  of  the  number  of  indi- 
viduals in  the  colony.  From  this  we  naturally  conclude  that  less  than 
1  per  cent  of  the  workers  can  keep  the  remainder,  including  the  queens 
and  immature  stages,  supplied  with  food.  These  observations  Were 
made  in  cases  where  the  food  supply  was  only  a  few  inches  from  the 
nest  and  was  always  in  abundance.  In  times  of  food  scarcity,  and 
when  it  is  necessary  for  the  workers  to  travel  considerable  distances  in 
order  to  reach  a  food  supply,  a  larger  percentage  would  have  to  engage 
in  foraging.  Observations  by  the  junior  author  upon  a  large  number 
of  field  colonies  leads  him  to  the  conclusion  that  even  under  the  most 
adverse  conditions  not  more  than  10  per  cent  of  the  workers  are 
required  for  foraging.  Under  normal  outdoor  conditions  the  food 
supply  is  abundant  and  at  such  times  it  is  very  doubtful  whether  more 
than  2  per  cent  of  the  workers  are  ever  engaged  in  foraging  at  any  one 
time.     The  futility  of  destroying  the  foraging  workers  is  therefore 


78  THE   ARGENTINE   ANT. 

self-evident,  for  the  number  of  workers  leaving  a  colony  during  any 
given  period  is  little  if  any  greater  than  the  number  reaching  maturity 
within  the  colony  during  the  same  period. 

In  spite  of  these  facts  repellents  are  very  desirable  and  their  use  is, 
under  most  conditions,  absolutely  imperative  in  the  protection  of 
foodstuffs,  such  as  sugars,  candies,  cakes,  molasses,  honey,  vegetable 
oils,  fresh  meats,  etc. 

EXPERIMENTS    WITH    REPELLENTS. 

Our  first  experiments  consisted  in  testing  the  various  substances 
which  had  been  used  in  successfully  repelling  other  species  of  ants. 

Experience  with  artificial  formicaries  and  with  the  hives  of  honey 
bees  very  quickly  showed  that  water  would  deter  the  workers  for  only 
a  short  time.  In  our  first  experiments  with  colonies  kept  under 
observation  the  nests  were  placed  on  platforms  supported  above  trays 
of  water.  As  soon  as  the  water  had  stood  for  a  few  hours  minute 
dust  particles,  settling  from  the  air,  formed  a  very  thin,  almost  imper- 
ceptible scum  on  it,  and  this  the  workers  traversed  with  ease.  A 
scum  which,  when  viewed  by  reflected  light,  is  barely  perceptible  to 
the  eye  will  support  the  workers.  When  such  standing  water  was 
removed  and  fresh  substituted  for  it  the  ants  would  plunge  into  it  as 
before,  evidently  expecting  the  scum  to  be  there  still.  Instead  of 
drowning,  as  might  be  expected,  the  workers  merely  swam,  or  crawled 
upon  the  bottom  of  the  tray  until  they  reached  the  edge  or  the  wooden 
support  of  the  nest,  when  they  proceeded  to  crawl  out.  Workers 
thrown  into  water  can  readily  crawl  up  one's  finger  or  up  a  stick  if  it 
is  brought  near  them.  The  senior  author  has  observed  workers 
which  had  accidentally  fallen  into  a  glass  decanter  three-fourths  full 
of  water  gain  a  foothold  on  the  smooth  glass  sides  and  crawl  out  suc- 
cessfully, feet  up  and  body  down,  on  the  wet  glass.  The  workers  will 
apparently  not  enter  fresh  water  voluntarily,  but  evidence  indicates 
that  they  will  sometimes  do  so  in  the  attempt  to  reach  their  nests  or 
to  reach  some  much-desired  food  supply.  When  running  over  a  film 
of  oil  or  dust  upon  the  water  the  feet  and  legs  do  not  get  wet,  but 
when  the  film  breaks  through,  as  sometimes  happens,  the  worker 
swims  with  her  legs  and  a  portion  of  the  body  submerged.  Running 
water,  such  as  a  stream  in  a  ditch  or  trough,  seems  to  be  a  successful 
repellent,  but  the  practical  uses  of  such  a  stream  are  very  limited. 
The  use  of  running  water  as  barriers  to  prevent  the  spread  of  infesta- 
tion in  orange  groves  is  more  fully  described  upon  a  subsequent  page. 

Sir  John  Lubbock  in  his  book,  "Ants,  Bees  and  Wasps,"  describes 
bands  of  fur  which  kept  the  ants  within  his  artificial  formicaries. 
The  kind  of  fur  used  by  Sir  John  Lubbock  is  not  specified,  but  the 
finest  we  were  able  to  secure  was  that  from  an  ordinary  " cottontail" 
rabbit.     With  this  the  following  experiment  was  made: 


METHODS    OF    REPRESSION.  79 

Two  devices  were  prepared,  each  consisting  of  a  small  wooden  box 
nailed  to  the  top  of  a  rounded  2-inch  stake  about  2  feet  in  length. 
Around  the  support  (stake)  of  one  box  a  roll  of  the  fur  was  tightly 
placed,  arranged  so  that  the  hairs  projected  downward  and  so  that  the 
ants  would  have  to  crawl  " against"  them  in  going  up  the  stake. 
Fur  was  not  placed  upon  the  other  device.  The  latter  was  stuck  in 
the  ground  and  a  supply  of  honey  placed  in  the  box.  The  ants 
visited  the  honey  at  once  and  as  fast  as  they  removed  it  the  supply 
was  renewed.  This  continued  for  several  days,  when  this  device  was 
removed  and  the  one  with  the  fur  was  put  in  its  place,  also  with  honey 
in  the  box.  The  interruption  of  the  " trail"  confused  the  ants  for  a 
little,  but  within  a  minute's  time  they  were  going  up  the  new  device 
and  working  their  way  persistently  among  the  hairs  of  the  fur.  In 
a  short  time  they  were  able  to  get  through  it,  when  they  continued  to 
the  food  supply  at  the  top  and  removed  it  as  before.  The  workers 
were  forced  to  make  their  way  slowly  through  the  fur,  wrestling  in 
turn  with  the  hairs  in  their  way,  but  at  most  the  fur  did  no  more  than 
delay  them  a  little;   it  did  not  repel  them  in  the  least. 

Various  experiments  were  made  with  certain  proprietary  and  coal- 
tar  disinfectants  for  protecting  food  supplies  from  the  ants.  Wood- 
work rubbed  or  painted  with  these  substances  was  not  crossed  by  the 
workers  during  periods  of  from  2  to  48  hours  after  the  applications, 
but  none  of  these  substances  was  effective  for  more  than  two  days. 
Oil  of  citronella  seemed  more  distasteful  to  the  ants  and  they  would 
not  cross  woodwork  treated  with  it  as  long  as  the  odor  remained. 
Evaporation  of  this  oil  is,  however,  quite  rapid. 

The  use  of  zenoleum  powder  was  found  quite  effective.  Sprinkled 
heavily  on  the  floors  of  infested  houses  it  killed  many  of  the  workers 
with  which  it  came  in  contact  and  answered  fairly  well  for  breaking: 
up  trails  and  causing  the  workers  to  seek  food  elsewhere.  It  was 
also  found  of  some  service  in  keeping  ants  out  of  the  nests  of  sitting 
hens. 

Pine  tar  was  not  effective.  In  an  attempt  to  feed  honey  to  bees  in 
the  open  air  the  feeder  was  supported  on  a  stick  around  which  were 
placed  two  separate  bands  of  fresh  pine  tar.  The  feeder  was  placed 
out  in  the  afternoon  and  by  6  o'clock  the  next  morning  the  ants  had 
crossed  both  bands  of  tar  and  the  honey  was  black  with  them.  To 
stop  them,  two  fresh  bands  of  tar  were  applied.  Within  30  minutes 
the  ants  which  were  trying  to  get  out  of  the  feeder  had  forced  their 
way  into  the  tar  in  sufficient  numbers  to  form  a  bridge  and  over  this 
the  ants  were  soon  passing  freely  to  and  fro,  despite  the  strong  odor 
of  the  tar  itself. 

The  following  experiment  proved  the  inefficiency  of  tobacco  dust: 
In  the  middle  of  a  large  iron  pan  with  flat  bottom  was  placed  a  dish 
of  honey.     This  dish  was  surrounded  by  a  layer  of  tobacco  dust  from 


80  THE    ARGENTINE    ANT. 

1  to  2  inches  wide  and  thick  enough  to  obscure  entirely  the  bottom  of 
the  pan.  This  arrangement  was  made  at  2  p.  m.,  and  by  5  p.  m.  the 
ants  were  crossing  the  tobacco  dust  and  getting  the  honey  with  as 
much  facility  as  they  would  have  crossed  an  equal  amount  of  soft  dirt. 
The  experiment  was  repeated,  finely  powdered  sulphur  being  substi- 
tuted for  the  tobacco.  The  sulphur  was  not  crossed  so  quickly  as  the 
tobacco  dust,  but  within  24  hours  the  ants  were  crossing  it  freely. 
On  one  occasion  the  senior  author  planted  a  small  lettuce  bed,  and 
thinking  to  protect  the  seeds  until  they  germinated,  he  spread  over 
the  surface  of  the  bed  a  layer  of  tobacco  dust  covered  in  turn  by  a 
layer  of  powdered  sulphur.     The  ants  got  the  seeds. 

Tree  tanglefoot,  wThen  placed  about  the  trunks  of  trees  up  w^hich 
the  ants  were  traveling,  checked  them  for  periods  varying  from  a  few 
hours  to  three  or  four  days.  HowTever,  a  more  dilute  form  of  this 
material,  used  with  much  success  in  the  gipsy  moth  work  in  Massa- 
chusetts by  Mr.  D.  M.  Rogers,  has  recently  been  tested  by  the  junior 
author  with  the  result  that  in  one  case  it  kept  the  ants  off  the  trees  for 
as  much  as  two  weeks  without  being  renewed.  There  is  therefore  a 
possibility  that  this  special  form  of  tanglefoot  may  have  a  use  in  the 
protection  of  trees. 

Kerosene  acts  as  a  repellent  until  the  odor  has  largely  disappeared, 
but  a  film  of  kerosene  on  wrater  only  affords  a  good  floor  for  the  ants 
to  travel  on. 

Various  devices  in  the  form  of  inverted  troughs  of  tin  or  other 
smooth  surfaces  have  been  tried  without  success. 

Crude  petroleum,  of  all  the  liquids  tested,  has  proved  to  be  the 
most  effective  repellent.  When  placed  in  dishes  supporting  the  legs 
of  tables,  benches,  etc.,  it  will  continue  to  repel  the  ants  even  after  a 
great  amount  of  dust  and  trash  has  accumulated  in  it.  Its  use 
indoors,  owing  to  its  oily  nature  and  disagreeable  odor,  is  of  course 
impracticable.  Out  of  doors  it  is  useful  for  giving  temporary  pro- 
tection to  such  food  materials  as  sugars,  molasses,  honey,  etc. 

CORROSIVE    SUBLIMATE    AND    "ANT  TAPES." 

The  only  repellent  found  to  possess  any  merit  (aside  from  sweetened 
arsenical  solutions,  described  below)  w^as  dry  corrosive  subUmate. 
Woodwork  or  cloth  wdiich  has  been  treated  with  a  saturated  wrater 
solution  of  corrosive  sublimate  and  allowed  to  dry  will  not  be  crossed 
by  the  ants  while  any  of  the  sublimate  remains.  This  fact  is  utilized 
in  a  practical  way  by  soaking  ordinary  cotton  tape  about  1  inch  wide 
in  the  corrosive  sublimate  solution,  wringing  it  out,  and  then  drying 
it.  When  this  "  ant  tape"  is  fastened  around  the  legs  of  tables,  edges 
of  shelves,  etc.,  the  ants  will  not  cross  it  for  many  months,  provided 
only  that  it  is  not  allowed  to  get  wet.  The  explanation  of  this  re- 
markable action  of  the  sublimate  may  be  found  in  the  extremely 


METHODS    OF    KEPKESSION.  81 

irritating  effect  which  it  has  on  tender  membranes  and  surfaces. 
The  finely  powdered  sublimate  and  the  minute  crystals  when  inhaled 
cause  a  severe  irritation  of  the  throat  and  nostrils,  giving  rise  to 
sneezing  and  nasal  discharges.  The  continued  or  careless  handling  of 
freshly  made  ant  tape  will  often  have  the  same  effect.  It  seems  not 
improbable  that  the  sublimate  particles  may  have  something  of  an 
irritating  effect  upon  the  sensory  organs  of  the  ants.  The  ants  are 
quick  to  detect  and  avoid  corrosive  sublimate  even  when  it  is  in  solu- 
tion and  mixed  with  other  substances.  All  attempts  to  poison  them 
with  this  substance  have  been  ineffectual,  for  they  can  not  be  induced 
to  partake  of  their  most  favorite  foods  when  the  latter  contain  the 
poison  in  as  weak  a  proportion  as  1  to  500. 

In  some  of  the  tests  made  by  the  senior  author  the  corrosive  subli- 
mate tape  has  been  found  to  retain  its  efficiency  for  over  11  months  in 
rooms  where,  except  when  the  temperature  was  too  low  for  insect 
activity,  workers  could  be  seen  at  all  hours  of  the  day  and  night. 

Our  method  of  preparing  the  tape  is  first  to  heat  corrosive  sublimate 
and  water  in  a  'porcelain  or  granite-ware  vessel  until  the  maximum 
amount  is  dissolved.  This  solution  is  allowed  to  cool  to  ordinary 
temperatures,  filtered,  and  ordinary  cotton  or  binding  tape  is  soaked 
in  it  for  several  hours.  The.  tape  is  then  removed  and  pinned  upon  a 
wall  to  dry,  after  which  it  is  ready  for  use.  It  is  very  important  that 
no  iron,  tin,  or  steel  come  in  contact  with  the  solution,  or  with  the 
tape  itself  after  being  prepared.  The  tape  is  effective  for  only  a  short 
time  when  used  on  metal  surfaces.  The  extremely  poisonous  nature  of 
corrosive  sublimate  must  be  continually  kept  in  mind,  both  in  the 
preparation  of  the  solutions  and  tape  and  in  the  use  of  the  tape  itself. 
With  this  tape  it  is  a  comparatively  easy  matter  so  to  isolate  dining 
tables,  kitchen  cabinets,  refrigerators,  etc.,  as  to  protect  all  food 
supplies  in  the  ordinary  residence.  The  same  method  is  constantly 
used  by  confectioners  in  infested  sections  for  the  protection  of  their 
candy  cases  and  supplies. 

EXPERIMENTS    WITH    FUMIGANTS    AND    CONTACT    INSECTICIDES. 

Following  the  announcement  by  Mr.  R.  S.  Woglum,1  of  the  Bureau 
of  Entomology,  in  September,  1908,  that  he  had  succeeded  in 
destroying  colonies  of  other  ants  with  a  solution  of  potassium 
cyanid,  considerable  interest  was  aroused  in  the  question  as  to 
whether  the  same  method  could  be  used  with  success  against  the 
Argentine  ant.  The  senior  author  conducted  a  number  of  experi- 
ments at  Baton  Rouge  to  determine  this  point,  among  which  the 
following  illustrates  the  results  obtained: 

i  Los  Angeles  Times,  Los  Angeles,  Cal.,  Sept.  20, 1908. 
75508°— Bull.  122—13 6 


82  -       THE   ARGENTINE    ANT. 

A  solution  of  potassium  cyanicl  was  made  at  the  strength  of 
1  ounce  of  98  per  cent  cyanicl  to  1  gallon  of  water.  The  site  selected 
for  the  experiment  was  the  area  surrounding  a  few  small  cotton 
plants  which  were  heavily  infested  with  the  cotton  louse,  Aphis 
gossypii  Glov.  Around  the  plants  the  earth  was  literally  honey- 
combed by  numerous  small  colonies  of  the  Argentine  ant,  the  workers 
of  which  were  in  constant  attendance  upon  the  aphides.  The 
experiment  was  made  at  11  a.  m.  on  a  bright  day,  with  the  tempera- 
ture at  about  77°  F.,  when  the  workers  were  busily  visiting  the  lice 
and  foraging  elsewhere  for  food  and  when  the  activities  of  the  colonies 
were  at  about  a  maximum.  The  solution  was  sprayed  onto  the 
trails  of  traveling  ants  and  the  ground  itself  was  sprayed  until 
thoroughly  wet  with  the  solution.  By  the  time  the  spraying  was 
completed  the  odor  of  the  cyanid  was  so  strong  as  to  affect  the 
operator.  In  spite  of  this  the  solution  did  not  immediately  kill  the 
workers  with  which  it  came  in  contact,  but  they  appeared  to  suc- 
cumb within  about  five  minutes  after  the  spraying.  Five  hours 
after  the  spraying  the  odor  of  cyanid  was  still  very  strong  and  the 
number  of  dead  workers  on  the  surface  of  the  ground  fully  equaled, 
or  exceeded,  the  number  of  living  ones  in  sight  at  the  time  of  spraying. 
Many  live  workers  were  busily  engaged  in  carrying  away  the  dead. 
The  ground  was  examined  and  thousands  of  living  ants  in  all  stages — 
workers,  pupre,  larva?,  and  eggs — were  found  less  than  half  an  inch 
below  the  surface.  Two  days  later  the  area  was  again  examined 
and  the  ant  colonies  were  apparently  as  populous  as  ever.  This 
and  other  experiments  seemed  to  demonstrate  the  impracticability 
of  using  this  solution  for  destruction  of  the  colonies,  particularly  as 
the  earth  would  have  to  be  treated  with  a  sufficient  amount  of  the 
solution  to  saturate  it  thoroughly  to  a  depth  of  several  inches.  This 
would  probably  destroy  all  vegetation,  would  be  expensive,  and 
would  involve  the  risk  of  injury  to  or  loss  of  life  by  the  operator  and 
others.  For  species  constructing  compact  nests  having  single  or 
few  openings  the  solution  is  doubtless  effective  but,  owing  to  the 
multitudinous  openings  and  galleries  of  the  Argentine  ant  nest, 
destruction  could  be  accomplished  only  by  the  use  of  enormous 
quantities  of  the  solution. 

The  resistance  of  this  species  to  hydrocyanic-acid  gas  was  well 
illustrated  in  experiments  made  in  attempting  to  fumigate  the 
winter  trap-boxes  in  orange  groves.  These  trap-boxes  are  described 
more  in  detail  on  pages  95-96.  They  were  about  2  feet  wide,  2  feet 
high,  and  3  feet  long,  made  of  rough  lumber  and  filled  with  decaying 
cottonseed  and  hay.  During  the  winter  months  these  boxes  con- 
tained enormous  colonies.  For  fumigating  them  to  destroy  these 
colonies  galvanized-iron  covers  were  made  (see  Plate  XII)  which 
would  fit  over  them  easily.     A  6-inch  hole  was  made  in  the  top  of  each 


METHODS   OF    REPRESSION.  83 

cover-box  for  tlie  introduction  of  the  chemicals  used  in  fumigating. 
Just  beneath  this  opening,  which  could  be  closed  practically  air-tight, 
was  placed  the  usual  earthenware  crock  for  holding  sulphuric  acid 
and  water.  Experimental  fumigation  of  these  boxes  was  commenced 
with  a  charge  of  i  ounce  of  98  per  cent  potassium  cyanid  and  the 
requisite  amounts  of  water  and  sulphuric  acid.  This  strength  was 
found  not  to  kill  any  ants  hi  the  box  except  those  which  were  actually 
outside  the  packing  at  the  time  of  fumigation.  Gradually  this 
charge  was  increased  until  as  much  as  4  ounces  of  cyanid  were  used 
at  a  time  in  the  inclosed  space  of  22  cubic  feet.  Even  at  this  strength, 
which  corresponded  to  18  ounces  of  cyanid  per  100  cubic  feet,  ants 
more  than  8  mches  from  the  outside  of  the  box  were  not  affected  by  a 
confinement  of  four  hours.  In  later  experiments  an  iron  rod  was 
used  to  make  holes  all  through  the  contents  of  the  box  and  the  same 
charge  used  as  before,  18  ounces  of  cyanid  per  100  cubic  feet.  After 
the  gras  had  been  confined  for  fixe  hours  the  boxes  were  examined 
and  it  was  found  that  only  those  within  a  couple  of  mches  of  the 
perforations  were  killed.  Larger  charges  could  not  be  used,  simply 
because  the  cover-box  would  not  contain  a  generator  of  sufficient 
capacity.  Even  had  a  charge  heavy  enough  for  effective  results 
been  found  its  cost  would  have  been  prohibitive  in  practical  field 
work. 

Experiments  were  accordingly  undertaken  with  bisulphid  of 
carbon  for  destruction  of  the  ants  in  the  boxes.  Holes  were  made  to 
the  very  bottom  of  the  contents,  bisulphid  poured  into  these,  and 
the  metal  cover  placed  over  the  box,  its  lower  edges  afterwards 
being  mounded  up  with  dirt.  One-half  pound  of  bisulphid,  used  in 
this  maimer  and  confined  by  the  metal  cover-box  for  five  hours, 
destroyed  all  ants,  and  all  stages,  hi  the  boxes.  Mention  is  made 
of  the  use  of  this  fumigant  on  page  96. 

Other  experiments  made  with  the  bisulphid  of  carbon  showed 
it  to  be  the  most  available  fumigant  for  the  destruction  of  colonies 
hi  accessible  situations. 

When  colonies  are  so  situated  that  they  can  be  fumigated  with 
bisulphid  nothing  is  more  effective  for  their  destruction,  but  the 
difficulty  of  applying  this  measure  lies  hi  the  situation  of  colonies 
in  all  sorts  of  inaccessible  places  (see  fist  of  nesting  places,  p.  55) 
and  to  the  fact  that  in  heavily  infested  areas  the  galleries  of  one 
nest  are  practically  continuous  with  those  of  others,  affording  many 
ants  the  opportunity  of  escaping  from  the  fumes. 

Such  substances  as  hot  water,  kerosene,  crude  oil,  etc.,  will,  of 
course,  destroy  the  ants  sprayed  with  them  and  often  it  is  quite 
practicable  to  use  these  substances  for  the  destruction  of  colonies 
that  are  discovered  by  turning  over  boards,  pieces  of  wood,  piles 
of  trash,  etc. 


84  THE   ARGENTINE   ANT. 

Many  preparations  have  been  sold  throughout  the  infested  sections 
for  the  purpose  of  destroying  the  ants.  In  nearly  all  cases  these 
have  been  merely  fluids  which  would  kill  the  ants  when  coming 
in  contact  with  them  and  the  directions  have  stipulated  that  the  ants 
should  be  sprayed  with  the  solutions  when  on  their  foraging  trails. 
In  view  of  the  foregoing  statements  relative  to  the  small  proportion 
of  workers  foraging  at  any  one  time  it  is  not  at  all  remarkable  that 
such  preparations  have  always  yielded  nothing  but  disappointment, 
even  though  enormous  numbers  of  foraging  workers  were  destroyed 
by  their  use. 

EXPERIMENTS    WITH    POISONS. 

The  use  of  poisons  is  generally  the  first  measure  suggested  for  the 
destruction  of  an  injurious  insect,  and  experiments  along  this  line 
were  begun  by  the  senior  author  early  in  the  course  of  his  investiga- 
tions. An  appreciation  of  the  salient  features  in  the  life  history  of 
the  pest  soon  emphasized  the  futility  of  using  a  poison  which  would 
destroy  the  workers  only.  Any  poison,  to  affect  the  rate  of  produc- 
tion or  to  exterminate  the  species,  must  be  one  winch  will  destroy  the 
fertile  queens  and  the  immature  stages,  all  of  winch  are  located  within 
the  nest  and  are  supplied  with  food  by  the  workers. 

Xo  way  could  be  devised  by  winch  poison  could  be  administered  to 
the  queens  and  larvae  except  by  having  the  workers  carry  it  to  them 
from  sources  of  supply  outside  the  nest  itself.  The  problem  therefore 
resolved  itself  into  the  search  for  some  poison  winch  would  be  fatal, 
but  winch  at  the  same  time  would  act  so  slowly  within  the  workers' 
stomachs  that  they  could  transport  it  to  the  colony  and  there  feed  it 
to  the  inmates  before  perishing  themselves. 

Some  small  measure  of  success  attended  our  experiments  in  this 
line  but,  incidentally,  another  and  much  more  valuable  use  for  poison- 
ous mixtures  was  discovered. 

Arsenate  of  lead,  containing  but  little  arsenic  in  soluble  form, 
naturally  suggested  itself  as  the  most  promising  substance  for  the 
purpose.  Accordingly  it  was  tried  in  various  experiments,  of  winch 
the  following  will  serve  to  illustrate  the  results  obtamed: 

A  mixture  was  made  of  1  part  pulverized  sugar,  1  part  paste 
arsenate  of  lead,  and  2  parts  of  honey.  The  ants  carried  this  away 
rapidly  and  on  August  11  exhausted  the  entire  amount  that  had  been 
put  out.  The  supply  was  renewed,  but  on  August  12  it  remained 
untouched.  An  examination  of  the  nest  was  then  made  and  it  was 
found  to  be  entirely  deserted;  the  colony  had  moved  away,  taking 
with  it  all  immature  stages.  That  this  action  had  been  taken  to  get 
outside  the  sphere  of  danger  from  the  poison  there  can  be  little  doubt, 
for  this  colony  had  occupied  the  same  spot  for  many  weeks,  despite 
the  fact  that  it  had  been  frequently  dug  open  for  examination  and 


METHODS   OF    REPRESSION.  85 

had  been  entirely  submerged  at  times  during  hard  rains.  No  dead 
ants  were  found  in  the  empty  nest ;  any  such,  if  present,  were  taken 
away  at  or  before  the  time  of  vacating  the  formicary.  The  ants  will 
not  tolerate  dead  within  their  living  chambers,  the  cadavers  always 
being  removed  expeditiously  and  often  to  a  considerable  distance. 
This  makes  it  extremely  difficult  to  tell,  by  examination  of  a  colony 
in  nature,  how  many  of  the  individuals  have  been  killed  by  any  poison 
fed  to  the  workers.  The  action  of  the  colon}"  in  moving  outside  the 
zone  of  danger  was  observed  in  many  subsequent  experiments  in 
which  poisoned  food  was  used,  and  tins  gave  us  the  clue  to  the  use  of 
sweetened  arsenical  mixtures  as  repellents  for  driving  the  colonies 
away  from  infested  situations.  The  same  phenomenon,  improperly 
understood,  has  been  responsible  for  the  conclusion,  arrived  at  by 
several  experimenters,  that  the  use  of  such  mixtures  was  actually 
exterminating  the  ants,  their  absence  after  use  of  the  poison  being 
ascribed  to  their  death  and  not  to  their  migration  to  a  safer  place. 

That  the  mixtures  containing  lead  arsenate,  such  as  those  just 
described,  do  destroy  the  individuals  within  the  nest  and  that  their 
continued  consumption  by  the  ants  would  result  in  extermination  if 
the  colony  did  not  move  away  from  them,  were  established  by  experi- 
ments made  with  colonies  kept  in  artificial  formicaries  where  migra- 
tion from  the  poison  was  made  impossible.  In  one  such  experiment 
a  small  amount  of  the  mixture  last  described  (1  part  lead  arsenate 
paste,  1  part  pulverized  sugar,  and  2  parts  honey)  was  kept  constantly 
on  the  food  table  of  a  colony  in  the  formicarium.  On  the  same  table, 
but  a  short  distance  from  it,  food  not  poisoned  was  also  kept  at  all 
times.  The  workers  from  tins  colony  therefore  had  their  choice 
between  poisoned  and  nonpoisoned  food.  A  few  workers  died  each 
day,  the  larvae  all  succumbing  a  few  days  after  inauguration  of  the 
experiment.  At  the  end  of  about  20  days  the  colony  seemed  demor- 
alized and  discouraged,  the  queen  ceased  to  lay,  and  the  workers  did 
not  work  with  their  accustomed  activity.  At  the  end  of  44  days  all 
individuals  were  dead,  the  queen  having  lived  until  near  the  end  of 
the  period. 

Many  solutions  and  mixtures  containing  white  arsenic  (arsenic 
trioxid)  were  tested  in  various  ways  and  the  one  winch  gave  by  far 
the  best  results  was  made  by  combining  one-fourth  gram  of  arsenic 
trioxid  with  20  grams  of  granulated  sugar  in  100  cc.  of  water.1  When 
placed  in  a  small  dish  anywhere  within  the  foraging  range  of  a  colony 
this  preparation  would  be  greedily  taken  for  a  few  hours,  after  winch 
the  ants  would  not  touch  it  as  long  as  it  remained  in  the  same  position. 
When  the  dish  was  moved  a  few  feet  away  or  placed  in  another  part 

1  To  give  warning  of  its  dangerous  nature  it  is  well  to  add  to  this  mixture  sufficient  confectioner's  color 
paste  to  dye  it  a  brilliant  red  or  green.  Fruit  juices,  as  of  raspberry  or  similar  fruits,  may  be  added  to 
accomplish  the  same  end. 


86  THE   ARGENTINE   ANT. 

of  the  same  room  and  "  rediscovered  "  by  the  workers  they  seemed  not 
to  recognize  its  dangerous  nature  and  would  take  it  as  before.  After 
a  few  experiences  of  this  kind  the  colony  would  move  away  from  the 
vicinity.  Only  in  rare  instances  were  these  migrations  actually  wit- 
nessed, as  they  seemed  usually  to  take  place  during  the  night.  A 
solution  containing  more  than  one-fourth  of  1  per  cent  of  arsenic  did 
not  give  as  good  results  for,  in  such  cases,  many  of  the  workers  died 
while  sipping  up  the  poison  or  on  their  way  to  the  colony.  Thus  the 
poisonous  nature  of  the  substance  was  more  quickly  detected  by  the 
ants  and  work  on  it  was  stopped  proportionately  sooner.  In  all  cases 
the  ants  removed  the  dead  and  dying  from  along  their  trails  and  from 
the  vicinity  of  the  poisoned  mixture. 

A  number  of  experiments  were  made  to  determine  whether  or  not 
the  ants  could  distinguish  between  poisoned  and  nonpoisoned  foods, 
with  the  result  that  they  evidently  could  not  do  so;  this  perhaps  being 
the  reason  that  they  moved  their  colonies  away  from  the  vicinity. 
One  of  these  experiments  was  as  follows: 

On  July  9  a  fruit  jar  containing  honey  was  placed  on  the  floor  of  a 
small  shed,  where  the  ants  had  been  very  abundant  for  weeks.  By 
the  f  olio  wing  day  all  honey  had  been  removed  by  the  workers  and  more 
was  placed  in  the  jar.  Between  the  9th  and  the  12th  the  jar  was 
replenished  several  times,  the  ants  during  this  time  carrying  away 
more  than  a  half  pint  of  honey.  At  noon  on  July  12  a  small  glass 
vessel  containing  a  mixture  composed  of  one-half  of  1  per  cent  of 
arsenic  and  20  per  cent  of  sugar  was  placed  about  3  inches  from  the 
honey  jar.  The  ants  commenced  taking  this  solution  at  once,  and 
in  the  course  of  five  minutes  the  vessel  was  black  with  them.  At  4 
p.  m.  on  the  same  day  they  were  still  working  with  undiminished 
vigor  on  both  the  honey  and  the  poisoned  solution.  At  8  a.  m.  on 
July  13  there  were  only  about  one-fourth  as  many  ants  visiting  the 
jars  as  on  the  previous  day.  They  were  still  working  on  both  the 
honey  and  the  solution  and  many  dead  ants  lay  about.  At  noon  of 
the  same  day  very  few  were  visiting  the  vessels,  but  many  were 
engaged  in  carrying  away  the  dead  bodies  of  their  erstwhile  sisters. 
A  few  were  still  taking  the  arsenic  solution,  but  it  was  evident  that  the 
ants  did  not  know  winch  of  the  food  supplies  was  destroying  them. 
At  2  p.  m.  on  July  14  only  two  workers  were  in  the  vicinity  of  the  ves- 
sels and  neither  of  these  was  feeding.  On  July  15  all  ants,  both  alive 
and  dead,  were  gone,  and  not  a  single  worker  could  be  found  in  the 
building.  Plenty  of  the  nonpoisoned  honey  still  remained  in  the  jar. 
On  July  16  and  17,  also,  no  ants  were  to  be  found  in  the  shed,  even 
though  heavy  rainstorms  in  the  meantime  drove  them  indoors  in 
many  other  buildings  and  decreased  their  available  outdoor  food  sup- 
ply. This  experiment  and  many  others  demonstrated  not  only  the 
effect  of  the  poison  in  driving  the  ants  from  the  vicinity,  but  also  that 


METHODS   OF   REPRESSION.  87 

food  supplies  could  be  protected  merely  by  having  the  poison  near 
them.  In  practical  work  it  was  found  that  the  placing  of  two  or  three 
saucers  containing  a  little  of  the  arsenical  solution  about  a  room  or 
under  tables  bearing  honey,  meats,  etc.,  would  effectually  rid  the 
vicinity  of  ants  in  from  one  to  three  days'  time,  and,  what  was  more  to 
the  point,  the  ants  would  not  return  in  numbers  so  long  as  the  dishes 
of  poison  were  kept  there. 

CONTROL    OF   THE    ANT    IN    RESIDENCES. 

No  one  measure  will  afford  satisfactory  relief  from  this  pest ,  and  the 
householder  who  would  find  permanent  immunity  from  attack  must 
plan  a  warfare  based  upon  an  intelligent  appreciation  of  the  facts 
above  set  forth.  Of  utmost  and  primary  importance  is  cleanliness. 
By  tins  is  meant  not  merely  absence  of  dirt  in  the  usual  sense,  but 
that  precautions  must  be  taken  not  to  leave  particles  of  food  where 
the  ants  can  have  access  to  them.  Even  crumbs  of  bread  or  cake 
left  on  a  kitchen  floor  will  attract  the  pests.  Above  all  else  fruits, 
sweets,  oils,  and  meats  must  be  kept  where  the  ants  can  not  reach 
them.  The  more  abundant  the  food  supply  the  more  abundant  will 
the  ants  become,  and  it  has  been  repeatedly  observed  that  there  are 
many  more  colonies  in  residences  occupied  by  shiftless  owners  than 
in  those  occupied  by  careful  housekeepers. 

Foodstuffs  can  not  be  isolated  from  the  ants  except  by  the  use 
of  repellents  such  as  have  been  described,  particularly  ant  tape. 
This  last  should  be  placed  around  the  legs  of  all  tables,  benches, 
etc.,  on  which  food  supplies  are  kept,  and  the  tables  must  not  be 
allowed  to  touch  the  wall  or  other  objects  by  means  of  which  the 
ants  can  find  access  to  them. 

The  corrosive  sublimate  tape  is,  of  course,  poisonous,  and  when 
there  are  children  in  the  house  precautions  must  be  taken  that  they 
do  not  get  hold  of  it.  At  the  same  time  we  have  never  known  of 
a  case  of  poisoning  resulting  from  its  use.  It  is  wise,  also,  to  wash 
the  hands  well  with  soap  and  warm  water  after  handling  the  tape. 

To  assist  in  repelling  the  ants  the  sweetened  arsenical  mixture, 
described  on  page  85,  containing  one-fourth  of  1  per  cent  of  arsenic, 
should  be  placed  in  small  dishes  or  saucers  in  pantries  and  beneath 
tables,  refrigerators,  etc. 

Along  with  these  repelling  measures  colonies  of  the  ants  should 
be  destroyed  at  every  opportunity.  Hot  water,  kerosene,  or  crude 
oil  can  be  used  for  destroying  every  colony  that  is  accidentally 
exposed  to  view  by  the  overturning  of  leaves,  boxes,  pieces  of  wood 
etc.  For  this  purpose  we  have  found  a  small  compressed-air  sprayer, 
filled  with  kerosene  or  crude  oil  and  kept  in  a  handy  place,  very 
useful.     Colonies  nesting  in  the  ground  can  be  quickly  destroyed 


88  THE    ARGENTINE    ANT. 

by  thrusting  a  sharp  stick  into  the  nest  and  pouring  in  a  sufficient 
amount  of  carbon  bisulphid  or  gasoline,  afterwards  closing  the  hole 
with  damp  earth. 

On  most  city  premises  the  ants  can  be  further  reduced  by  making 
use  of  winter  trap  nests  or  trap  boxes,  such  as  are  described  on  pages 
95-96  under  the  caption  "Experiments  with  winter  trap  boxes. " 

Mention  should  not  be  omitted  at  this  point  of  the  steps  advocated 
by  the  Rev.  Albert  Biever,  of  Loyola  College,  New  Orleans,  who, 
by  his  constant  advocacy  of  warfare  against  this  pest,  did  much 
to  enlighten  the  people  of  New  Orleans  concerning  it.  Father 
Biever's  plan  was  to  place  sponges  moistened  with  sweetened  water 
in  locations  visited  by  the  ants,  and  when  these  were  covered  with 
the  pests  to  dip  them  into  boiling  water.  The  sponges  were  then 
recharged  and  the  process  repeated  as  long  as  the  ants  would  visit 
them.  By  this  persistent  destruction  of  the  workers  Father  Biever 
expected  so  to  deplete  the  colony  that  not  enough  workers  would 
remain  to  care  for  the  queens  and  larvae  and  the  latter  would  perish 
from  starvation. 

A  most  novel  way  of  destroying  these  ants  was  described  by  Mr. 
Edwyn  C.  Reed,  of  the  Museo  de  Concepcion,  Concepcion,  Chile, 
in  a  letter  to  the  senior  author.     Mr.  Reed  says: 

The  only  sure  cure  would  be  to  take  Biblical  measures  and  root  up  the  city  infested, 
stone  by  stone,  and  strew  it  with  salt.  As  such  a  radical  cure  is  not  practical,  we  must 
be  content  with  palliatives,  and  I  find  the  following  very  effective:  This  ant  is  very 
fond  of  olive  oil,  and  so,  in  sardine  tins,  saucers,  etc.,  I  put  a  little  olive  oil  in  its  runs. 
The  ants  flock  to  the  oil  and  in  eating  it  get  clogged  up,  so  that  for  a  spoonful  of  oil 
I  get  about  that  quantity  of  ants,  dead  and  harmless.  In  practice  this  so  weakens 
the  nests  that  I  get  rid  of  them.  Last  November  I  moved  into  a  house  sadly  infested 
by  them  and  at  once  applied  the  oil.  They  came  to  it  by  thousands  and  stayed 
there.  In  a  month's  time  I  could  appreciate  the  result,  and  by  the  end  of  our  southern 
summer  very  few  were  to  be  seen. 

CONTROL    OF   THE    ANT    IN   APIARIES. 

The  keeping  of  bees  is  made  well-nigh  impossible  in  sections 
heavily  infested  by  the  Argentine  ant.  Single  colonies  of  the  ants 
often  contain  more  individuals  than  a  colony  of  bees,  and  in  addition 
the  colonies  of  ants  are  by  far  the  most  numerous.  The  Argentine 
ants  are  not  only  exceedingly  fond  of  honey  but  they  attack  the 
bee  larvae  in  the  cells  with  a  ferocity  that  is  amazing.  Thousands 
upon  thousands  of  the  ants  will  enter  the  hive,  carrying  away  honey 
and  attacking  the  larvae.  The  bees  themselves  are  unable  to  cope 
with  such  small  enemies.  The  ants  are  too  small  for  them  to  sting 
and  were  they  even  to  attempt  picking  up  the  ants  in  their  mandibles 
and  carrying  them  out  of  the  hive  they  could  make  no  appreciable 
headway  against  the  thousands  of  intruders.  The  bees  adopt  what 
is  perhaps  the  best  method  of  defense  under  the  circumstances,  that 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  VII 


4  \ 

_■/  I 

|^  ' ■■■■fljfflfftftjl 


Beehive  on   Ant-Proof  Hive  Stand,  the  Latter  Resting  Upon  a  Concrete  Block. 

(Original.) 


METHODS   OF   REPRESSION.  89 

of  trying  literally  to  kick  out  the  invaders.  A  worker  bee  will  run 
in  among  the  ants  and,  whirling  about,  will  give  repeated  vigorous 
kicks  with  her  hind  legs,  throwing  the  ants  in  every  direction,  even 
to  a  distance  of  10  or  12  niches.  The  ants  are  not,  however,  killed 
by  tins  rough  treatment,  and  they  shortly  return  to  the  attack. 
In  a  few  hours  after  the  attack  has  commenced  the  bees  become 
thoroughly  disorganized  and  give  up  further  defense,  sometimes 
swarming  out  as  a  last  resort.  At  such  times  the  normal  hum  of 
the  hive  gives  place  to  an  entirely  different  note,  which  the  expe- 
rienced bee  keeper  at  once  recognizes  as  that  of  distress. 

The  difficulties  of  extracting  and  handling  honey  in  the  presence 
of  these  pests  can  be  readily  imagined.  In  order  to  extract  we 
first  scrubbed  the  floor  of  the  building,  using  copious  amounts  of 
carbolic  acid  in  the  water.  The  foundations  of  the  building  and 
a  space  about  a  foot  wide  all  around  the  building  were  then  sprayed 
with  crude  oil.  The  extractor,  as  well  as  the  uncapping  can,  was 
placed  hi  a  large  iron  tray  containing  several  niches  of  water.  When 
all  these  preparations  were  complete,  the  supers  were  taken  from 
the  hives,  and  as  fast  as  brought  hi  were  stacked  on  tables  the  legs 
of  which  were  wound  with  the  corrosive  sublimate  ant  tape.  Extract- 
ing was  done  as  expeditiously  as  possible,  but  with  all  our  pains 
the  ants  were  all  over  everything  before  we  could  extract  and  bottle 
three  or  four  hundred  pounds  of  honey.  Even  our  clothing  was 
teemhig  with  the  workers  and  all  human  effort  was  helpless  to  keep 
them  out  of  the  honey. 

The  number  of  apiaries  destroyed  by  the  ant  in  southern  Louisiana 
has  been  considerable,  and  one  of  our  first  lines  of  experimental 
work  was  to  devise  some  means  of  protecting  the  beehives  from  the 
foraging  ants.  Among  the  various  schemes  that  were  tried  the 
folio  whig  were  found  most  efficient : 

Placing  the  hive  upon  a  stand  having  four  legs  and  placing  each 
of  these  legs  hi  a  thi  cup  containing  crude  petroleum  served  to  deter 
the  ants  for  a  time,  but  rain  water  soon  displaced  the  oil  in  the  cups, 
and  then  with  the  first  accumulation  of  dust  on  the  water  the  ants 
found  then*  way  across  it.  This  device  also  had  the  disadvantage 
of  killing  all  bees  winch  attempted  to  crawl  up  the  legs  of  the  stand. 

Another  device,  somewhat  more  successful  than  the  open  cups, 
consisted  of  a  stand  the  legs  of  which  had  at  then  tops  inverted 
troughs  of  galvanized  iron  so  arranged  that  ram  water  could  not 
enter  them,  and  so  fixed  that  the  ants  would  have  to  cross  the  troughs 
containing  oil  in  order  to  reach  the  hive.  Stands  protected  with 
this  appliance  successfully  repelled  all  ants  for  about  two  months 
but,  like  the  open  cups  of  oil,  resulted  hi  the  death  of  some  bees. 

As  our  previous  experiments  had  shown  the  repellent  power  of 
ant  tape,  already  described,  it  occurred  to  us  that  tins  might  be 


90 


THE   ARGENTINE  ANT. 


used  in  the  construction  of  an  ' k  ant-proof  "  hive  stand.  Accordingly 
a  four-legged  hive  stand  was  made  with  top  and  sides  extending 
some  distance  beyond  the  legs  and  downward,  so  as  to  prevent  rain 
water  from  reaching  the  upper  end  of  each  leg.  The  top  and  sides 
were  made  thoroughly  water-tight  and  the  ant  tape  wound  several 
tunes  about  the  upper  end  of  each  leg.  Below  the  tape,  fitting 
snugly  around  the  leg,  was  a  piece  of  zinc  about  6  inches  square  to 
prevent  water  from  splashing  upward  from  the  ground  during  storms. 
One  of  these  hive  stands,  turned  on  end  to  show  the  method  of 
construction,  is  illustrated  in  figure  11,  and  the  details  of  construc- 
tion are  further  shown 
in  figures  12  and  13. 
These  figures  are  from 
drawings  by  Miss  Ethel 
Hutson.  The  two  front 
legs  of  the  stand  were 
made  an  inch  shorter 
than  the  rear  two  to 
give  proper  drainage  to 
the  hive.  In  putting  on 
the  tape  we  wrapped 
about  a  yard  of  tape 
about  each  leg,  placing 
corrosive  sublimate  be- 
tween the  layers.  Made 
in  this  manner  these 
stands  by  actual  test 
repelled  all  ants  for  11 
months  without  any 
attention  being  re- 
quired except  to  pre- 
vent grass  and  weeds 
from  growing  up  and 
touching  the  hive  and 
upper  part  of  the  stand. 
With  corrosive  sub- 
limate between  the 
layers  of  tape  the  latter  is  effective  until  it  disintegrates  or  until  it 
gets  wet,  and  bees  crawling  up  the  legs  pass  the  barrier  of  tape 
without  injury  or  inconvenience.  Our  stands  were  made  of  tongue- 
and-groove  lumber,  which  made  them  rather  cumbersome,  but  there 
is  no  reason  why  such  stands  should  not  be  made  with  top  and  sides 
of  galvanized  iron.  This  would  make  them  light,  durable,  and 
cheap. 


Fig. 11. 


-Ant-proof  hive  stand,  upturned,  showing  method  of  con- 
struction.    (Senior  author's  illustration.) 


METHODS    OF    REPRESSION. 


91 


In  spite  of  the  fact  that  the  hive  stand  was  absolutely  ant  proof 
we  experienced  much  difficulty  in  preventing  grass  from  growing  up 
under  the  hives  and  affording  a  passageway  for  the  ants.  To  elimi- 
nate this  difficulty  we  covered  the  entire  apiary  with  about  5  inches 
of  cinders  and  placed  each  hive  stand  upon  a  concrete  block.  (See 
Plate  VII.) 

Rev.  Albert  Biever,  S.  J.,  devised  a  unique  method  of  protecting  his 
bees  from  the  ants.     This  method  he  describes  as  follows : 

Blocks  of  wood  are  obtained,  upon  which  the  legs  of  the  bee  stand  rest.  Then  the 
cover  of  a  lard  can  or  large  tin  box  sufficiently  wide  when  placed  in  an  inverted  posi- 
tion on  top  of  the  blocks  will  overlap  the  block  of  wood  on  all  sides.  A  paste  con- 
sisting of  vaseline  mixed  with  kerosene  and  red  pepper  is  then  spread  thinly  over 
the  inside  of  the  can  or  cover,  and  the  ants  will  never  be  able  to  reach  the  legs  of  the 
stand  and  gain  access  to  the  hives.  An  advantage  of  this  method  is  that  the  paste 
need  not  be  renewed  more  than  once  every  year  or  two,  and,  being  protected  from  the 
weather,  it  can  not  be  washed  off. 

One  can  successfully  keep  a  few  colonies  of  bees  in  any  portion  of  the 
ant-infested  area  by 


zzu 


making  use  of  the  spe- 
cial stands  described 
above,  but  eternal  vig- 
ilance is  the  price  of 
success,  for  when  the 
ants  do  gam  access 
to  the  bees  the  latter 
are  likely  to  be  dis- 
organized within  a 
few  hours  and  the 
swarms  will  abscond. 
Along  with  the  use  of 
the  ant-proof  stands  one  should  also  use  every  means  for  reducing 
the  ant  colonies  in  the  vicinity  of  the  apiary. 

The  commercial  apiarist  can  hardly  continue  keeping  bees  with 
profit  after  his  apiary  is  invaded  by  this  pest,  the  amount  of  labor  in 
constructing  hive  stands  and  keeping  down  vegetation  being  almost 
prohibitive.  In  such  cases  the  wisest  course  would  be  to  remove  the 
entire  apiary  to  some  locality  where  these  ants  do  not  occur.  As 
already  noted,  the  infestation  is  not  infrequently  confined  to  cities 
and  towns,  and  small  rural  sections  still  free  from  this  pest  can  usually 
be  found  within  driving  distance. 


Fig.  12.— Sectional  view  of  ant- proof  hive  stand,  showing  method  of 
making  top  and  sides  water-tight  by  '•  breaking"  the  faints.  (Sen- 
ior author's  illustration. ) 


CONTROL  OF  THE  ANT  IN  ORANGE  GROVES. 

The  main  orange-growing  section  of  Louisiana  lies  along  the  banks 
of  the  Mississippi  Kiver  below  New  Orleans  and  extends  for  a  distance 
of  about  50  miles.     This  section  has  the  reputation  of  producing 


92 


THE   ARGENTINE  ANT. 


oranges  of  exceptionally  high  quality,  and  the  industry  has  proven  a 
paying  one  for  many  years  past.  A  considerable  number  of  localities 
have  during  the  past  15  or  20  years  become  infested  by  the  Argentine 
ant,  due,  no  doubt,  to  drifting  logs  containing  ant  colonies  that 
lodged  along  the  banks  of  the  river.  The  warm  winters,  coupled  with 
the  presence  of  considerable  moisture  at  all  times,  have  made  possible 
very  rapid  increase  of  the  ants,  and  the  first  result  of  their  activities 
has  been  a  greatly  accelerated  rate  of  increase  by  all  scale  insects,  and 
particularly  by  the  chaff  scale  (Parlatoria  pergandii  Comst.).  Not 
only  do  the  ants  protect  this  scale  from  its  natural  enemies,  but  they 

colonize  the  larvae  up- 


1 1" 

i 


\tm 


x 


on  the  young  growth 
of  the  orange  trees  and 
upon  trees  not  pre- 
viously infested. 

At  times  the  ants 
eat  into  the  orange 
buds,  evidently  in 
quest  of  nectar,  and 
buds  thus  injured  do 
not  set  fruit.  This 
habit  is  not  always 
exhibited  by  the  ants, 
and  it  may  be  that  it  is 
more  or  less  dependent 
upon  the  prevalence 
of  scale  insects  on  the 
trees.  The  secretions 
of  aphides  and  scale 
insects  are  preferred 
to  other  food,  and  it 
seems  not  unlikely 
that  when  honeydew 
is  abundant  the  buds  are  not  molested  by  the  ants.  Whether 
or  not  the  ants  do  any  other  direct  damage  to  the  trees  is  still 
an  unsettled  question,  but  certain  it  is  that  the  bearing  qualities 
of  an  orchard  are  seriously  impaired  by  the  second  season  of 
infestation,  the  crop  is  almost  entirely  lost  by  the  third  season, 
and  the  trees  are  dying  rapidly  by  the  fourth  year  of  infesta- 
tion. (See  PI.  VIII.)  One  orchard  which  well  illustrates  the  rate 
of  destruction  consisted  of  a  20-acre  tract  of  young  grapefruit 
trees,  visited  by  the  authors  in  March,  1910.  The  trees  at  this 
time  were  about  4  to  5  feet  in  height  and  appeared  very  vigorous  and 
healthy.  The  ants  were,  however,  rapidly  infesting  the  field  from 
adjoining  orchards.     During  the  summer  of  1910  the  ants  increased 


Fig. 13. 


-Sectional  view  of  ant-proof  hive  stand  from  above,  show- 
ing construction.     (Senior  author's  illustration.) 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  VIII. 


Bui.  122,  Eureau  of   Entomology.  U.  S.  Dept.  of  Agriculture. 


Plate  IX. 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  X. 


h 


mm 

mm 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  XI. 


Bridges  which  the  Argentine  Ant  Can  Not  Cross.    (Original.) 


METHODS   OF   REPRESSION.  93 

rapidly,  as  did  the  Lecaniums,  which  were  constantly  attended  by 
the  ants.  The  owner  sprayed  industriously  with  whale-oil  soap,  but 
without  apparent  effect.  During  1911  many  of  the  trees  died,  and 
at  the  present  time  (March,  1912)  the  orchard  is  practically  ruined 
and  the  owner  has  abandoned  hope  of  saving  enough  trees  to  make  the 
orchard  profitable.  The  condition  of  dying  trees  is  well  illustrated 
by  Plate  VI,  which  shows  a  Louisiana  Sweet  orange  tree  that  has  been 
exposed  to  ant  infestation  for  three  seasons.  This  tree  stood  near  the 
levee,  outside  the  barrier  ditches  described  below,  and  was  exposed  to 
the  work  of  the  ants. 

Another  orange  orchard  which  we  have  had  under  close  observation 
has  been  infested  for  7  years,  and  during  this  time  no  measures  have 
been  taken  to  control  the  ants.  In  this  orchard  fully  60  per  cent  of 
the  trees  are  dead  and  the  remaining  trees  are  heavily  incrusted  with 
both  the  chaff  scale  and  the  purple  scale  (LepidosapJies  hechii  Xewm.). 
So  abundant  are  the  ants  here  that  a  bit  of  earth  disturbed  by  one's 
foot  at  any  point  in  the  orchard  will  reveal  a  seething  mass  of  ants. 
A  recent  crop  from  this  orchard  consisted  of  but  250  boxes  of  inferior 
quality.  Other  orchards,  of  approximately  the  same  size  but  not  yet 
infested  by  the  ant,  produced  in  the  neighborhood  of  3,000  boxes. 
At  Soccola  Canal  there  is  a  small  tract  of  land  on  which  four  orange 
orchards  have  been  planted  in  succession,  all  of  which  have  died  before 
reaching  bearing  age.  The  entire  neighborhood  is  heavily  infested, 
and  Mr.  S.  M.  O'Brien,  of  Nairn,  La.,  states  that  to  his  knowledge  the 
ants  have  been  abundant  at  Soccola  for  at  least  17  years.  The  plat 
has  now  been  entirely  abandoned  as  an  orange  grove,  the  last  of  the 
dead  orchards  having  been  removed  during  1911  and  the  land  devoted 
to  the  growing  of  truck  crops. 

METHOD    OF   DISSEMINATION    IX   THE    ORANGE    SECTION. 

As  already  indicated,  the  most  probable  sources  of  original  infesta- 
tions in  the  orange  section  were  drifting  logs  in  the  river,  these  logs 
carrying  living  colonies  of  the  Argentine  ant.  In  times  of  flood  these 
logs  are  thrown  up  on  the  batture  (the  space  between  the  river  bank 
and  the  levee)  and  remain  there  in  large  numbers.  It  is  the  history 
of  practically  all  infestations  in  this  section  that  the  ants  first  appeared 
on  the  batture,  then  along  the  levee,  and  from  the  latter  worked  their 
way  back  from  the  river.  At  all  the  infested  points  the  levee  is  found 
to  be  teeming  with  the  ants  and  the  batture  itself  is  a  constant  breed- 
ing place.  A  portion  of  the  infested  batture,  covered  with  a  thick 
growth  of  willows,  is  shown  in  Plate  IX.  Here  the  ant  colonies  are 
found  under  every  particle  of  driftwood  and  trash,  and  during  almost 
the  entire  year  they  are  in  attendance  upon  Coccidae  and  Aphididaa 
on  the  willows.  For  a  number  of  weeks  each  year  this  batture  is 
covered  with  several  feet  of  water  from  the  river,  but  the  infestation 


94  THE   ARGENTINE   ANT. 

seems  not  to  be  lessened  thereby.  During  flood  time  many  of  the  ant 
colonies  migrate  to  the  levee  adjoining,  while  still  others  ascend  the 
trees  out  of  the  water's  way.  Curious  nests  or  sheds,  constructed 
by  the  ants  from  particles  of  earth  and  trash,  are  of  common  occur- 
rence in  the  tops  of  the  willow  trees. 

In  some  few  places  it  is  evident  that  the  railroad  has  been  the  means 
of  introduction,  the  infestation  having  started  at  points  on  the  railroad 
where  considerable  merchandise  from  New  Orleans  was  constantly 
being  unloaded. 

EXPERIMENTS  IN  THE  ORANGE  GROVES. 

The  writers'  first  experiments  with  the  pest  in  orange  groves  were 
commenced  in  the  spring  of  1910.  At  that  time  only  one  grower  in 
the  Louisiana  orange  section  was  attempting  anything  like  a  system- 
atic campaign  against  the  ants.  This  grower  had  adopted  a  novel 
and  rather  effective  method  of  destroying  them.  The  infested  por- 
tion of  his  orchard  immediately  adjoined  the  levee  and,  as  is  usual 
with  land  along  the  river,  was  lower  by  several  feet  than  the  water  in 
the  river  during  flood  stages.  The  water  could  therefore  be  siphoned 
over  the  levee  to  the  orchard  as  rapidly  as  needed.  (See  PI.  X.)  To 
prevent  the  spread  of  the  ants  to  additional  territory  the  infested 
block  had  been  surrounded  by  a  ditch,  a  section  of  which  may  also  be 
seen  hi  Plate  X,  in  which  water  was  kept  at  all  times.  During  flood 
stages  of  the  river  the  water  was  siphoned  over  for  the  ditches  at  small 
expense  and  through  the  ditch  system  drained  away  to  the  swamp  in 
the  rear  of  the  plantation.  At  other  times  the  water  was  kept  in  the 
"ant  ditches"  by  use  of  a  gasoline  engine  and  pump  installed  on  the 
levee,  as  shown  in  Plate  X.  It  was,  of  course,  necessary  to  take  pre- 
cautions that  the  ants  should  not  find  accidental  and  artificial  means 
of  crossing  the  ditches.  Permanent  bridges  for  the  passage  of  teams 
could  not  be*left,  so  a  swinging  bridge  which  could  be  lifted  when  not 
in  use  was  devised.  The  ditching  system  for  preventing  spread  of  the 
ants  was  shortly  adopted  by  many  other  growers,  some  of  whom  used 
an  ingenious  divided  bridge  (PL  XI)  which  could  be  crossed  readily 
by  teams,  but  which  had  a  2-inch  crack  through  the  middle  that  effec- 
tually prevented  the  passage  of  the  ants. 

The  grower  referred  to  had  put  in  practice  the  following  method  of 
destroying  the  ants:  A  small  levee  or  ridge  was  made  around  the 
infested  block  of  trees.  Water  was  then  admitted  through  the  siphon 
from  the  river  until  the  ground  in  the  block  was  entirely  covered.  As 
the  water  slowly  rose  the  colonies  of  ants  moved  up  into  the  orange 
trees.  Then  the  water  was  drawn  off  and  the  ants,  descending,  found 
the  ground  still  too  wet  to  live  in,  whereupon  they  migrated  en  masse 
to  the  surrounding  small  levee.  The  water  was  then  turned  on  for 
the  second  time  to  keep  the  ants  on  this  ridge,  and  here  they  were 


METHODS    OF    REPRESSION.  95 

destroyed  by  exposing  the  colonies  with  a  shovel  and  scalding  them 
with  hot  water  or  spraying  them  with  kerosene.  At  the  senior 
author's  suggestion  a  number  of  small  boxes  filled  with  hay  and  trash 
were  placed  at  various  points  in  the  orchard.  When  the  water  was 
admitted  it  was  found  that  the  colonies  moved  into  these  boxes  in 
preference  to  going  up  the  trees.  They  could  thus  be  destroyed  with 
one  flooding  instead  of  two,  as  formerly. 

It  may  be  remarked  in  passing  that  the  ditches,  when  pains  have 
been  taken  to  prevent  the  ants  crossing  them,  have  effectively  limited 
the  spread  of  the  ants  through  the  groves.  This  fact  amply  substan- 
tiates our  observations,  mentioned  on  pages  19-20,  to  the  effect  that 
colonies  are  never  established  by  individual  queens  returning  from  a 
marriage  flight.  Were  colonies  established  in  tins  manner,  the  areas 
of  infestation  would  not  be  sharply  defined,  nor  would  ditches  retard 
the  dispersion  of  the  ants  from  heavily  infested  centers. 

EXPERIMENTS    WITH    WINTER    TRAP    BOXES- 

The  success  which  had  followed  experiments  at  Baton  Rouge  in 
getting  the  ant  colonies  to  concentrate  during  the  winter  in  boxes 
of  decaying  vegetable  matter  induced  us  to  try  the  same  plan  in 
an  infested  orange  grove.  Accordingly  in  November,  1910,  a  large 
number  of  boxes,  each  2  by  2  by  3  feet,  of  rough  lumber,  were  made 
and  distributed  throughout  the  infested  block.  Each  was  filled, 
during  the  latter  part  of  October,  with  a  mixture  of  cotton  seed  and 
dead  grass.  The  top  of  each  box  was  left  exposed  to  the  weather, 
so  that  rain  would  enter  to  moisten  the  contents  and  start  decay. 
An  examination  of  the  boxes  on  November  16  showed  that  many 
colonies  had  entered  them,  but  that  many  still  remained  in  the 
ground.  To  afford  the  ants  less  natural  protection  the  orchard  was 
cultivated  to  remove  the  standing  grass  and  weeds.  In  January, 
1911,  the  authors  again  visited  this  orchard  and  found  all  boxes 
filled  almost  to  overflowing  with  enormous  ant  colonies.  Each  box 
contained  workers  by  the  hundreds  of  thousands  and  queens  by  the 
hundreds.  A  close  examination  in  various  parts  of  the  orchard 
showed,  however,  that  not  all  colonies  had  entered  the  boxes.  Some 
few  colonies  had  remained  in  their  underground  nests,  particularly 
where  grass  or  weeds  had  been  overlooked  in  the  November  cultiva- 
tion and  where,  therefore,  these  colonies  were  afforded  more  protec- 
tion than  in  the  plowed  portions.  Whether  the  already  crowded 
condition  of  the  boxes  had  prevented  other  colonies  from  entering 
them  we  could  not  determine. 

Experiments  were  now  undertaken  in  destruction  of  the  colonies 
in  the  boxes.  Metal  covers  had  already  been  constructed  for  con- 
fining gases  in  the  trap  boxes.     (See  PL  XII.)     Experiments  were 


96  THE   ARGENTINE   ANT. 

first  made  in  fumigating  the  boxes  with  hydrocyanic-acid  gas  (see 
pp.  82-83),  but  these  were  not  successful.  Carbon  bisulphid  was  next 
tried,  with  perfect  success.  Delay  in  obtaining  a  sufficient  supply 
of  bisulphid  resulted  in  delayed  treatment  of  many  of  the  boxes, 
and  doubtless  some  of  the  colonies  escaped  as  the  weather  became 
warmer  in  the  early  part  of  February.  Nevertheless,  the  number 
of  queens  and  workers  destroyed  ranged  into  the  millions.  The 
owner  wished  to  deal  the  ants  the  hardest  blow  possible,  so  early 
in  the  spring  he  flooded  the  orchard,  drove  the  remaining  ant  colo- 
nies to  the  boxes,  and  fumigated  these  the  second  time. 

The  results  of  this  work  were  eminently  satisfactory.  The  orchard 
was  first  infested  by  the  ants  in  1909.  In  1910  they  reached  enor- 
mous numbers;  chaff  and  purple  scales  increased  until  the  trees  were 
almost  encrusted,  and  many  of  the  trees  showed  signs  of  failing. 
The  foliage  began  to  turn  yellow,  and  the  crop  of  1910  fell  off 
severely,  in  spite  of  the  flooding  that  was  done  by  the  owner  in  the 
spring  of  1910.  During  the  summer  of  1911,  following  the  use  of 
the  trap  boxes,  the  orchard  improved  remarkably,  and  the  crop  was 
up  to  the  original  production.  It  was  found  that  when  the  boxes 
were  left  in  the  orchard  ant  colonies  took  up  their  abode  therein 
during  the  summer  months;  for  this  reason  these  boxes  were  fumi- 
gated with  bisulphid  from  time  to  time.  An  examination  of  the 
orchard  in  January,  1912,  showed  that  the  infestation  by  the  chaff 
scale  had  been  greatly  reduced  by  diminution  of  the  ants,  even 
though  the  owner  had  done  no  spraying  for  destruction  of  the  scale 
insects.  The  ant  infestation  showed  some  increase  in  the  autumn 
of  1911,  but  the  orchard  had  returned  to  its  normal  healthy  condi- 
tion, and  it  was  evident  that  a  continuation  of  these  methods  would 
insure  good  crops  indefinitely.  A  view  of  this  orchard,  taken  in 
January,  1912,  is  shown  in  Plate  XIII. 

One  important  point  came  to  light  in  these  experiments,  and  that 
was  the  necessity  of  placing  the  trap  boxes  in  position  early  in  the 
autumn  so  that  the  vegetation  in  them  would  be  decaying  well  at 
the  approach  of  cool  weather  in  November.  With  considerable 
decomposition  going  on  at  the  time  the  ants  are  seeking  winter 
quarters,  the  warmth  of  the  box  becomes  very  attractive  to  them. 

The  use  of  arsenicals  and  other  poisons  in  the  infested  orange 
groves  was  found  impossible,  for  the  reason  that  the  secretions  of 
scale  insects  and  aphides  are  preferred  by  the  ants  to  all  other  foods. 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  XII. 


Bui.  122,  Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture. 


Plate  XIII. 


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